fix: allow building aws images using source_ami

[supershal]

What problem does this PR solve?:
Packer fails building AMI when user provides source_ami instead of source_ami_filters
Packer fails when evaluating empty ami_filter string: ""
error:

2023/03/09 03:54:12 starting packer build
Error: Datasource.Execute failed: Couldn't parse ami filters: EOF

related upstream issue: hashicorp/packer#11037
Fix:

• set the ami_filter to empty block {} when source_ami is provided.
• the packer ami datasource requires owner field. so setting it to self in case user does not provide it or explicitly set it to empty (""). see https://developer.hashicorp.com/packer/plugins/builders/amazon/ebs#owners

This is a special usecase that our e2e tests does not cover.
I verified the fix by testing manually.

Which issue(s) does this PR fix?:

*https://d2iq.atlassian.net/browse/D2IQ-96305

Special notes for your reviewer:

Packer uses HCL2 for its configuration language. This is same language used in Terraform. however, it is more restrictive when used with packer. This makes it difficult to write conditional blocks.
Other options considered:

• use count to control block execution. This is most preferred way in terraform HCL. This does not work with Packer.
  error: An argument named "count" is not expected here
  reference: Conditional data sources? hashicorp/packer#11483 (comment)

• use dynamic blocks
  documentation: https://developer.hashicorp.com/terraform/language/expressions/dynamic-blocks
  This solution works at some extent to render empty data resource.
  However the source_ami_filter block requires owner field which makes it difficult to completely omit the data resource for ami.

• use local variables
  Packer does not support using local variables in data resource block. makes it difficult to create conditional variables.
  Packer issue: Data Sources cannot use local values hashicorp/packer#11011

• Use Go template
  9b53818
  We have used go template before. While this is a great solution, we will end up with mix of go templates and raw packer files. Raw packer files has advantage of testing them directly without getting rendered by KIB. which makes it easy to iterate when triaging bugs.

[dlipovetsky]

HCL has a https://en.wikipedia.org/wiki/Ternary_conditional_operator? 😱

[msdolbey]

👍
Thanks! Let me know when merged, and I'll be able to check it out!

[dkoshkin]

Tested locally passing source AMI

➜  konvoy-image-builder git:(shalin/fix-ami-source) ✗ ./bin/konvoy-image-wrapper build aws --overrides overrides/fips.yaml images/ami/rhel-84-fips.yaml --source-ami ami-07da62bb37a54c3b7
2023/03/09 21:03:57 writing new packer configuration to work/rhel-8.4-fips-1678395837-fZfQj
2023/03/09 21:03:57 starting packer build
amazon-ebs.kib_image: output will be in this color.

==> amazon-ebs.kib_image: Prevalidating any provided VPC information
==> amazon-ebs.kib_image: Prevalidating AMI Name: konvoy-ami-rhel-8.4-fips-1.25.4-fips.0-20230309210405
    amazon-ebs.kib_image: Found Image ID: ami-07da62bb37a54c3b7
    ...