Improve Container Image OCI Metadata and Versioning

[tekenstam]

What this PR does / why we need it

This PR enhances our container image builds with proper OCI metadata and improved versioning to better support multi-architecture images and provide clearer traceability.

Changes made

1. GitHub Actions Workflow:

   • Implemented proper annotation-index syntax for multi-architecture manifest annotation
   • Fixed metadata placeholders to use GitHub context variables that properly resolve

2. Makefile:

   • Added OCI label support to local container builds
   • Improved versioning with INSTANCEMGR_TAG that includes:
     • Latest Git tag (e.g., v0.19.0)
     • Short commit SHA (e.g., 9835017)
     • Dirty flag (-dirty) when there are uncommitted changes

How to verify it

• Container images now display proper metadata in both DockerHub and GitHub Container Registry
• Locally built images using make docker-build have consistent metadata with CI-built images
• The versioning scheme allows for better traceability back to source code

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 46.13%. Comparing base (49204ce) to head (2ae5c16).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #480   +/-   ##
=======================================
  Coverage   46.13%   46.13%           
=======================================
  Files          40       40           
  Lines        7004     7004           
=======================================
  Hits         3231     3231           
  Misses       3617     3617           
  Partials      156      156           

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