Support username/password authentication

[ire4ever1190]

Implements #256

Supports connecting via basic auth if the instance supports it.
Configured via either

• Environment variables
  • GRAFANA_USERNAME
  • GRAFANA_PASSWORD
• HTTP Headers using standard HTTP basic auth

Works locally when connecting to grafana instance that has basic auth

[CLAassistant]

All committers have signed the CLA.

[sd2k]

This looks great, thank you! The one thing I'd love to see is an end-to-end test. I think it should be possible to:

• set GF_AUTH_ANONYMOUS_ENABLED: "false" in our docker-compose file
• modify the code that creates a new test context to set the basic auth (admin/admin) on the client used by integration tests
• update the e2e.yml GitHub workflow to set the env vars for the Start MCP server in background step

I know it's a bit annoying to run these e2e tests since they require OpenAI/Anthropic usage so I can add this in a separate PR if you like, just let me know.

(Also, the e2e tests are failing right now, they're a bit flaky depending on how the LLMs are feeling on the day, so don't worry about those failures)

[ire4ever1190]

Thanks for explaining! Will add it in this PR

[ire4ever1190]

I was able to get integration running locally, e2e just wasn't happy though (Got litellm to the local qwen model that I use but did not work well...)

[sd2k]

Nice, this looks and works great. Thank you @ire4ever1190!

One request, could you update the test-python-e2e target in the Makefile so that it runs something like:

	cd tests && uv sync --all-groups
	cd tests && GRAFANA_USERNAME=admin GRAFANA_PASSWORD=admin uv run pytest

[ire4ever1190]

Nice, this looks and works great. Thank you @ire4ever1190!

One request, could you update the test-python-e2e target in the Makefile so that it runs something like:

	cd tests && uv sync --all-groups
	cd tests && GRAFANA_USERNAME=admin GRAFANA_PASSWORD=admin uv run pytest

Thanks! Completed in latest commit