Add assertion doc job

[ciarams87]

Proposed changes

Problem: We need to add the generation and publishing of a signed assertion document to our workflow. The goal of the signed assertion document is to provide a customer facing document that provides provenance for a build artifact. The document will contain information about each dependency included in the build and specifically will contain the signed acquisition document for each process. This will also be signed to guarantee that F5 is the source of the document.

Solution: Use the actions provided by compliance-rules to generate and sign the assertion document

Testing: See https://github.com/nginx/nginx-gateway-fabric/actions/runs/18093624043/job/51480400063

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

Release notes

If this PR introduces a change that affects users and needs to be mentioned in the release notes,
please add a brief note that summarizes the change.

NONE

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.77%. Comparing base (a2ee4c4) to head (bd529ba).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3929      +/-   ##
==========================================
- Coverage   86.82%   86.77%   -0.06%     
==========================================
  Files         128      128              
  Lines       16607    16607              
  Branches       62       62              
==========================================
- Hits        14419    14410       -9     
- Misses       2005     2012       +7     
- Partials      183      185       +2     

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[jjngx]

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