Add release notes generator script using litellm

scripts/make_release_notes.py fetches a GitHub release body and commit
history via the gh CLI, resolves author logins, then calls any LLM
supported by litellm (Anthropic Claude, Google Gemini, etc.) to produce
categorised, author-attributed release notes in Markdown.

Fetched data is cached in RELEASE_DATA_<version>.json so subsequent
runs (e.g. trying a different model or revised prompt) skip all GitHub
API calls.  Use --no-cache to force a fresh fetch.  The --model flag
accepts any litellm model string such as gemini/gemini-2.5-flash or
anthropic/claude-opus-4-7.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Co-Authored-By: Himanshu Gohel <1551217+hgohel@users.noreply.github.com>

Author: 3 people