GitHub Action: azure/setup-cosmosdb-shell for CI workflows

[sajeetharan]

Feedback source

External user feedback (travel multi-agent workshop team).

Problem

There is no official GitHub Action to install/setup CosmosDB Shell in CI workflows. Users must manually download, extract, and add to PATH — adding boilerplate and fragility to every workflow.

Proposed solution

Publish an official azure/setup-cosmosdb-shell GitHub Action that:

• Accepts a version input (with a sensible default/latest)
• Downloads the correct platform-specific package
• Extracts and adds to PATH
• Caches the binary across runs (using actions/cache or tool-cache)
• Verifies checksum/signature

Example usage

steps:
  - uses: azure/setup-cosmosdb-shell@v1
    with:
      version: 1.0.213-preview
```n
## Acceptance criteria
- [ ] Action published to GitHub Marketplace
- [ ] Supports Linux, macOS, Windows runners
- [ ] Built-in caching (tool-cache pattern)
- [ ] Version pinning and 'latest' support
- [ ] Documented in CI/CD guide