Add release automation script

[svekars]

• Adds .release/release_docs.py which automates the mechanical steps of the PyTorch documentation release checklist
• Covers three phases: enable-nightly (after first RC), pre-release (a few days before release), and post-release (day after release)
• Handles cross-repo changes in pytorch/docs (pytorch-versions.json, stable symlink, noindex tags) by shallow-cloning, committing, and pushing branches
  • Includes validation for pytorch-versions.json (schema checks, duplicate detection, preferred flag)
  • Safe to re-run: cleans up stale branches and handles no-op cases gracefully

What it automates

• Enabling/disabling nightly CI workflow triggers
• Updating torch version pins in requirements.txt and .jenkins/build.sh
• Adding RC and stable entries to pytorch-versions.json in pytorch/docs
• Updating the stable symlink in pytorch/docs
• Running add_noindex_tag.sh for the previous version in pytorch/docs
• Running lintrunner after local changes (if available)

What it does NOT automate

• Merging PRs (you create, review, and merge manually)
• Updating ecosystem package versions (torchrl, torchao, etc.)
• Updating the "What's New" section in index.rst

Test plan

• Run python .release/release_docs.py --phase list to verify help output
• Run --phase enable-nightly with --cuda and verify workflow YAML, build.sh, and pytorch-versions.json changes
• Run --phase pre-release and verify 4 PRs are created (1 tutorials + 3 docs)
• Run --phase post-release and verify workflow is disabled and docker requirements updated
• Run with --clean flag to verify stale clone is removed
• Re-run a phase to verify idempotent behavior

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/tutorials/3832

• 📄 Preview Python docs built from this PR

Note: Links to docs will display an error until the docs builds have been completed.

❌ 1 New Failure

As of commit e59b62d with merge base f6afe53 ():

NEW FAILURE - The following job has failed:

• link check on PR / linkChecker (gh)
  Process completed with exit code 1.

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