feat: add ec2_sd_configs in ScrapeConfig

[slashpai]

Fixes #5818

Not all fields are implemented, current change will support monitoring using API access and secret key

Description

Describe the big picture of your changes here to communicate to the maintainers why we should accept this pull request.
If it fixes a bug or resolves a feature request, be sure to link to that issue.

Add EC2 Service Discovery support in ScrapeConfig

This is how I tested the change:

• Created an ec2 instance, added security group to open port 9100, installed node-exporter and run it

• Attached the policy AmazonEC2ReadOnlyAccess to IAM credentials (reference)

• Created k8s secret with api access key and secret key

• Created ScrapeConfig with EC2SDConfig

  apiVersion: monitoring.coreos.com/v1alpha1
  kind: ScrapeConfig
  metadata:
    name: scrape-config-ec2
    namespace: default
    labels:
      app.kubernetes.io/name: scrape-config-ec2
  spec:
    ec2SDConfigs:
      - region: us-east-1
        accessKey:
          key: accessKey
          name: aws-api-access
        secretKey:
          key: secretKey
          name: aws-api-access
        port: 9100
    relabelings:
    - sourceLabels: [__meta_ec2_public_ip]
      replacement: ${1}:9100
      targetLabel: __address__

  Relabelling was required because only public ip will be accessible to scrape target metrics

Result:

I added unit tests, I am exploring how to do e2e test using localstack but that will take some time to explore in free time

Type of change

What type of changes does your code introduce to the Prometheus operator? Put an x in the box that apply.

• CHANGE (fix or feature that would cause existing functionality to not work as expected)
• FEATURE (non-breaking change which adds functionality)
• BUGFIX (non-breaking change which fixes an issue)
• ENHANCEMENT (non-breaking change which improves existing functionality)
• NONE (if none of the other choices apply. Example, tooling, build system, CI, docs, etc.)

Changelog entry

Please put a one-line changelog entry below. This will be copied to the changelog file during the release process.

Add EC2 Service Discovery support in ScrapeConfig

[slashpai]

Please have another look on this :)

[slashpai]

addressed comments