fix: DBTP-1789 - Remove required pipelines config

[JohnStainsby]

Addresses https://uktrade.atlassian.net/browse/DBTP-1789

• If no pipelines are listed don't deploy event bridge triggers
• The additional_ecr_repository expects different formats e.g. demodjango/application for private repos or public.ecr.aws/uktrade-platform-sandbox/demodjango/application for public
  • Make the image exists check work with public and private ECR images
  • Ensure the correct IAM permissions are in place for public and private additional repos
• Tidy up unnecessary pipelines variables

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Checklist:

Title:

• Scope included as per conventional commits
• Ticket reference included (unless it's a quick out of ticket thing)

Description:

• Link to ticket included (unless it's a quick out of ticket thing)
• Includes tests (or an explanation for why it doesn't)
• Includes any applicable changes to the documentation in this code base
• Includes link(s) to any applicable changes to the documentation in the DBT Platform Documentation (can be to a pull request)

Tasks:

• Trigger the pull request regression tests for this branch and confirm that they are passing

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.68%. Comparing base (51ee145) to head (2b31cf1).

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #338   +/-   ##
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  Coverage   81.68%   81.68%           
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  Files           7        7           
  Lines         868      868           
=======================================
  Hits          709      709           
  Misses        159      159           

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[JohnStainsby]

Large diff because I've added extra test blocks for the additional_ecr_repo being public/private.
Also split out the big env var blocks to test individual variables.

[WillGibson]

Great to see the more targeted, hopefully less brittle, testing of the environment variables.

A couple of questions, but neither are blockers for me so approving.