fix: Automate versioned documentation publication

[larrysingleton007]

What this PR does / why we need it:

Minor releases currently finish without creating their maintenance branch or advancing the public GitBook version. This adds a post-release job that creates or verifies the version branch, imports it into GitBook, publishes it, and confirms it became the default.

The release workflow can also publish documentation for an existing release without rerunning the release jobs. Maintainers provide the released version and can preview the operation with the default dry-run setting before publishing. The standalone path does not move stable or create a release.

The helper is safe to rerun. It reuses matching resources, refuses to move a conflicting maintenance branch, and keeps the previous documentation default until the new import succeeds. The release guide now covers the required GitBook configuration, standalone publishing, and manual recovery path.

Which issue(s) this PR fixes:

Fixes #6762

Checks

• I've made sure the tests are passing.
• My commits are signed off (git commit -s)
• My PR title follows conventional commits format

Testing Strategy

• Unit tests
• Integration tests
• Manual tests
• Testing is not required for this change

Ran the 10 focused unit tests, Ruff, repository pre-commit hooks, YAML parsing, a credential-free v0.66.0 dry run, and git diff --check. Live GitBook validation still requires a maintainer-owned test site and scoped token.

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 47.08%. Comparing base (f0bc070) to head (dd06b84).
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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6763      +/-   ##
==========================================
- Coverage   47.09%   47.08%   -0.01%     
==========================================
  Files         419      419              
  Lines       51878    51878              
  Branches     7525     7525              
==========================================
- Hits        24430    24429       -1     
  Misses      25700    25700              
- Partials     1748     1749       +1     

Flag	Coverage Δ
go-feature-server	30.58% <ø> (ø)
python-unit	48.39% <ø> (-0.01%)	⬇️
see 1 file with indirect coverage changes

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[larrysingleton007]

v0.66.0 shipped while this PR was open and reproduced the gap it addresses. The release and version branch succeeded, but the public docs root and /v0.66-branch/ currently return 404. The old /v0.64-branch/ and /master/ paths still return 200, so the current v0.66 GitBook default needs a manual repair.

I merged current upstream master into this branch and reran the 10 focused tests, Ruff, pre-commit, YAML parsing, and the dry run. They pass, and PR CI has restarted.

@franciscojavierarceo @ntkathole, could one of you review the future-release automation when you have a chance?

[ntkathole]

looks good

[larrysingleton007]

Added the standalone publish option discussed in Slack. Setting publish_docs_version skips the release jobs and runs only the documentation publisher, with dry-run enabled by default. It does not move stable or create a release. The v0.66.0 dry run and all 10 focused tests pass locally. @ntkathole, please take another look at the new workflow path when CI finishes.