Migrate Homebrew formula generation from abandoned `homebrew-pypi-poet` to Homebrew's built-in tooling

### Current State
The Azure CLI's Homebrew formula generation pipeline uses [`homebrew-pypi-poet`](https://github.com/tdsmith/homebrew-pypi-poet), which:
- Was last updated in **2018** (8 years ago)
- Uses the deprecated `pkg_resources` API (removed in setuptools 82+)
- Has an [open issue from 2023](https://github.com/tdsmith/homebrew-pypi-poet/issues/74) recommending deprecation
- Forces us to pin `setuptools<82` in the Homebrew Docker environment

### Why This Matters
1. **Technical debt**: We're pinning core dependencies to old versions to support abandoned tooling
2. **Maintenance burden**: Each setuptools upgrade requires checking compatibility
3. **Security & stability**: Can't take advantage of setuptools improvements and fixes
4. **Homebrew evolution**: We're not using the officially supported workflow

### Temporary Fix (Already Implemented)
Added `setuptools<82` to `scripts/release/homebrew/docker/requirements.txt` to unblock builds. This is **isolated to the formula generation container only** and doesn't affect Azure CLI itself.