PYTHON-5579 Add AI-Generated Contributions Policy

[Jibola]

PYTHON-5579

Changes in this PR

Contribution policy and documentation updates:

• Added a comprehensive AI-generated contributions policy in docs/internals/contributing/ai-contributions-policy.rst

• Updated reference to point to docs/internals/contributing/index.rst.

• Added a new CONTRIBUTING.md file with clear guidelines on submitting issues, bug fixes, and large code changes, and referenced the full contribution guidelines in the documentation.

• Updated .github/PULL_REQUEST_TEMPLATE.md to require PR titles in a specific format and to include a note about the AI contributions policy, ensuring contributors are aware of the new requirements.

Test Plan

N/A

Checklist

Checklist for Author

• [n/a] Did you update the changelog (if necessary)?
• [n/a] Is there test coverage?
• [n/a] Is any followup work tracked in a JIRA ticket? If so, add link(s).

Checklist for Reviewer

• Does the title of the PR reference a JIRA Ticket?
• Do you fully understand the implementation? (Would you be comfortable explaining how this code works to someone else?)
• Is all relevant documentation (README or docstring) updated?

[timgraham]

I'd prefer a minimal CONTRIBUTING.md similar to Django's with a reference to the contributing documentation which is all-inclusive. Here's how similar info is organized in Django docs: https://docs.djangoproject.com/en/dev/internals/contributing/writing-code/submitting-patches/#ai-assisted-contributions

[Jibola]

I'd prefer a minimal CONTRIBUTING.md similar to Django's with a reference to the contributing documentation which is all-inclusive. Here's how similar info is organized in Django docs: https://docs.djangoproject.com/en/dev/internals/contributing/writing-code/submitting-patches/#ai-assisted-contributions

I can agree with this. I'll make the structural change.