Add comprehensive release process documentation

[vhaasteren]

Summary

This PR adds detailed documentation for the enterprise release process, which is fully automated but was not clearly documented.

Changes Made

• Added RELEASE.md: Comprehensive release documentation including:
  • Fully automated release process via GitHub Actions
  • Explanation of trusted publishing setup
  • Version management via setuptools_scm
  • Troubleshooting and release checklist
• Updated CONTRIBUTING.rst: Added "For Maintainers" section with link to release documentation

Release Process Documented

• Fully automated PyPI uploads via GitHub Actions
• Trusted publishing (no API tokens needed)
• Version management via setuptools_scm (automatic from git tags)
• GitHub environment configuration requirements

Benefits

• Clear understanding of the automated process
• Documentation of trusted publishing approach
• Easier troubleshooting when issues arise
• Better maintainer onboarding

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.58%. Comparing base (90dfa56) to head (bf6286d).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #427   +/-   ##
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  Coverage   71.58%   71.58%           
=======================================
  Files          13       13           
  Lines        3245     3245           
=======================================
  Hits         2323     2323           
  Misses        922      922           

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