[checks] make api-endpoint parameter optional & update usage docs

[kylos101]

Description

It is only necessary for customers to specify a value for api-endpoint when the VPC endpoints are not in the same account as Gitpod.

Related Issue(s)

Fixes CLC-1118

How to test

Test w/o api-endpoint param, it should not be included in the results for the main subnet
Test w/ api-endpoint param, it should be included in the results for the main subnet
See test results (below)

Documentation

/hold

[kylos101]

Test w/o the api-endpoint param:

go run . diagnose
INFO[0000] ℹ️  Running with region `eu-central-1`, main subnet `[subnet-02a57899464adb227  subnet-013003bf204f47611]`, pod subnet `[subnet-0f59b6bfead78792c  subnet-0d6ae7d559bcf50db]`, hosts `[accounts.google.com  https://github.com]`, and api endpoint `` 
INFO[0000] ✅ Main Subnets are valid                     
INFO[0000] ✅ Pod Subnets are valid                      
INFO[0000] ℹ️  Checking prerequisites                   
INFO[0000] ℹ️  VPC endpoint com.amazonaws.eu-central-1.ec2messages is not configured, testing service connectivity... 
INFO[0000] ✅ Service ec2messages.eu-central-1.amazonaws.com has connectivity 
INFO[0000] ℹ️  VPC endpoint com.amazonaws.eu-central-1.ssm is not configured, testing service connectivity... 
INFO[0000] ✅ Service ssm.eu-central-1.amazonaws.com has connectivity 
INFO[0000] ℹ️  VPC endpoint com.amazonaws.eu-central-1.ssmmessages is not configured, testing service connectivity... 
INFO[0000] ✅ Service ssmmessages.eu-central-1.amazonaws.com has connectivity 
INFO[0000] ✅ VPC endpoint com.amazonaws.eu-central-1.execute-api is configured 
INFO[0000] ✅ IAM role created and policy attached       
INFO[0001] ℹ️  Launching EC2 instances in Main subnets  
INFO[0001] ℹ️  Created security group with ID: sg-084cfa567812a6bf2 
INFO[0001] ℹ️  Instance type t2.micro shall be used     
INFO[0009] ℹ️  Created security group with ID: sg-0a96a5a8299d4738f 
INFO[0009] ℹ️  Instance type t2.micro shall be used     
INFO[0010] ℹ️  Main EC2 instances: [i-0fac3db35493cb297 i-080ee8342d5f7a1d7] 
INFO[0010] ℹ️  Launching EC2 instances in a Pod subnets 
INFO[0011] ℹ️  Created security group with ID: sg-09df3743501aba525 
INFO[0011] ℹ️  Instance type t2.micro shall be used     
INFO[0013] ℹ️  Created security group with ID: sg-095604552846531bf 
INFO[0014] ℹ️  Instance type t2.micro shall be used     
INFO[0015] ℹ️  Pod EC2 instances: [i-0f347cec110371841 i-08d28c247fd2edd02] 
INFO[0015] ℹ️  Waiting for EC2 instances to become ready (can take up to 2 minutes) 
INFO[0020] ✅ EC2 Instances are now running successfully 
INFO[0020] ℹ️  Connecting to SSM...                     
INFO[0107] ℹ️  Checking if the required AWS Services can be reached from the ec2 instances in the pod subnet 
INFO[0107] ✅ Autoscaling is available                   
INFO[0108] ✅ CloudFormation is available                
INFO[0109] ✅ CloudWatch is available                    
INFO[0110] ✅ EC2 is available                           
INFO[0111] ✅ EC2messages is available                   
INFO[0112] ✅ ECR is available                           
INFO[0113] ✅ ECR Api is available                       
INFO[0114] ✅ EKS is available                           
INFO[0115] ✅ Elastic LoadBalancing is available         
INFO[0116] ✅ KMS is available                           
INFO[0117] ✅ Kinesis Firehose is available              
INFO[0117] ✅ SSM is available                           
INFO[0118] ✅ SSMmessages is available                   
INFO[0120] ✅ SecretsManager is available                
INFO[0121] ✅ Sts is available                           \

INFO[0121] ℹ️  Checking if certain AWS Services can be reached from ec2 instances in the main subnet 
INFO[0122] ✅ DynamoDB is available                      
INFO[0122] ✅ S3 is available                            

INFO[0122] ℹ️  Checking if hosts can be reached with HTTPS from ec2 instances in the main subnets 
INFO[0124] ✅ accounts.google.com is available           
INFO[0125] ✅ https://github.com is available            
INFO[0125] ✅ Instances terminated                       
INFO[0125] Cleaning up: Waiting for 2 minutes so network interfaces are deleted 

No ExecuteAPI ref in main subnet tests.

[kylos101]

Test results with execute api:

go run . diagnose
INFO[0000] ℹ️  Running with region `eu-central-1`, main subnet `[subnet-02a57899464adb227  subnet-013003bf204f47611]`, pod subnet `[subnet-0f59b6bfead78792c  subnet-0d6ae7d559bcf50db]`, hosts `[accounts.google.com  https://github.com]`, and api endpoint `xxxxx` 
INFO[0000] ✅ Main Subnets are valid                     
INFO[0000] ✅ Pod Subnets are valid                      
INFO[0000] ℹ️  Checking prerequisites                   
INFO[0000] ℹ️  VPC endpoint com.amazonaws.eu-central-1.ec2messages is not configured, testing service connectivity... 
INFO[0000] ✅ Service ec2messages.eu-central-1.amazonaws.com has connectivity 
INFO[0000] ℹ️  VPC endpoint com.amazonaws.eu-central-1.ssm is not configured, testing service connectivity... 
INFO[0000] ✅ Service ssm.eu-central-1.amazonaws.com has connectivity 
INFO[0000] ℹ️  VPC endpoint com.amazonaws.eu-central-1.ssmmessages is not configured, testing service connectivity... 
INFO[0000] ✅ Service ssmmessages.eu-central-1.amazonaws.com has connectivity 
INFO[0000] ✅ VPC endpoint com.amazonaws.eu-central-1.execute-api is configured 
INFO[0000] ✅ IAM role created and policy attached       
INFO[0001] ℹ️  Launching EC2 instances in Main subnets  
INFO[0001] ℹ️  Created security group with ID: sg-02bbceec8996d72c5 
INFO[0002] ℹ️  Instance type t2.micro shall be used     
INFO[0009] ℹ️  Created security group with ID: sg-0074a57eb3072312c 
INFO[0009] ℹ️  Instance type t2.micro shall be used     
INFO[0010] ℹ️  Main EC2 instances: [i-05dc4d216fc716800 i-026df99a5dafde253] 
INFO[0010] ℹ️  Launching EC2 instances in a Pod subnets 
INFO[0011] ℹ️  Created security group with ID: sg-01c7d23c48f57e621 
INFO[0011] ℹ️  Instance type t2.micro shall be used     
INFO[0013] ℹ️  Created security group with ID: sg-0ff845be60326e32d 
INFO[0014] ℹ️  Instance type t2.micro shall be used     
INFO[0015] ℹ️  Pod EC2 instances: [i-05b28f65aaa6397e4 i-0f59eaef3b54e3cf1] 
INFO[0015] ℹ️  Waiting for EC2 instances to become ready (can take up to 2 minutes) 
INFO[0027] ✅ EC2 Instances are now running successfully 
INFO[0027] ℹ️  Connecting to SSM...                     
INFO[0112] ℹ️  Checking if the required AWS Services can be reached from the ec2 instances in the pod subnet 
INFO[0113] ✅ Autoscaling is available                   
INFO[0114] ✅ CloudFormation is available                
INFO[0115] ✅ CloudWatch is available                    
INFO[0117] ✅ EC2 is available                           
INFO[0118] ✅ EC2messages is available                   
INFO[0118] ✅ ECR is available                           
INFO[0119] ✅ ECR Api is available                       
INFO[0120] ✅ EKS is available                           
INFO[0121] ✅ Elastic LoadBalancing is available         
INFO[0122] ✅ KMS is available                           
INFO[0123] ✅ Kinesis Firehose is available              
INFO[0124] ✅ SSM is available                           
INFO[0126] ✅ SSMmessages is available                   
INFO[0126] ✅ SecretsManager is available                
INFO[0127] ✅ Sts is available                           

INFO[0127] ℹ️  Checking if certain AWS Services can be reached from ec2 instances in the main subnet 
INFO[0127] ✅ DynamoDB is available                      
INFO[0129] ✅ ExecuteAPI is available                    <--- it worked
INFO[0130] ✅ S3 is available                            

INFO[0130] ℹ️  Checking if hosts can be reached with HTTPS from ec2 instances in the main subnets 
INFO[0131] ✅ accounts.google.com is available           
INFO[0132] ✅ https://github.com is available            
INFO[0132] ✅ Instances terminated                       
INFO[0132] Cleaning up: Waiting for 2 minutes so network interfaces are deleted 

[kylos101]

Enabled auto merge