Update release process documentation

[Yonghui-Lee]

This PR extracts the release process documentation into a dedicated docs/source/release.rst and updates it to detail the automated monthly release process introduced in #916.

[gemini-code-assist]

Code Review

This pull request refactors the documentation by moving the release process details from developer.rst into a new dedicated release.rst file and updating the index. The review feedback points out several instances in the new file where nested lists are not separated from their preceding paragraphs by a blank line, which is required in reStructuredText to prevent Sphinx build warnings or parsing errors.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.68%. Comparing base (1b08827) to head (826d8bd).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #945   +/-   ##
=======================================
  Coverage   89.68%   89.68%           
=======================================
  Files          16       16           
  Lines        3579     3579           
=======================================
  Hits         3210     3210           
  Misses        369      369           

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