Add MCP tool to create Grafana annotations

It would be great to have an MCP tool to create Grafana annotations, which would be a very useful feature. This would allow users troubleshooting issues with Claude.ai or ChatGPT to immediately create annotations marking important timelines or events without needing to switch to the Grafana dashboard.

https://grafana.com/docs/grafana/latest/developers/http_api/annotations/