Add CI pipeline to mass‑regenerate api.md using azpysdk apiview --md

[swathipil]

Title

Add CI pipeline to mass‑regenerate api.md using azpysdk apiview --md

Summary

Add a CI pipeline that automatically regenerates api.md across Python packages using azpysdk apiview --md and opens a draft PR when changes are detected.
This pipeline should run when the apistub version changes (and be runnable manually).

Proposed Implementation (Actionable)

1. Create a new pipeline

   • Location: eng/*/jobs
   • Linux only
   • PR triggers disabled

2. Configure triggers

   • CI trigger path scoped to the file that bumps eng/apiview_reqs.txt
   • Allow manual runs

3. Pipeline steps

   • Checkout repo
   • Install azure-sdk-tools
   • For each Python package:
     • Run:

       azpysdk apiview --md

       to regenerate api.md
   • After all packages complete:
     • Run git diff
     • If no diffs → exit successfully
     • If diffs exist → continue

4. Create a draft PR

   • Use the existing create-pull-request YAML template
   • Open a draft PR back to the repo
   • PR should contain only api.md changes

5. Parallelism

   • Use dispatch / parallel jobs for per‑package generation to keep runtime reasonable

Non‑Goals

• No manual per‑package updates
• No APIView UI or review flow changes

Acceptance Criteria

• Linux pipeline added under eng/*/jobs
• Pipeline runs on apistub version changes in eng/apiview_reqs.txt and manually
• api.md generated via azpysdk apiview --md
• Draft PR opened only when diffs exist
• PR contains only api.md updates