Authenticated Prometheus requests

[emschwartz]

The extension should support using basic auth to authenticate with Prometheus. We may also want to support other auth mechanisms to talk to other hosted Prometheus-compatible solutions

If we support multiple environments (https://github.com/autometrics-dev/vscode-autometrics/discussions/26), we should also think about how to have the auth details on a per-environment basis.

[arendjr]

What milestone do you think we should apply? It sounds like something a lot of people may need, so attaching to 1.0 may make sense, I think.

[emschwartz]

Makes sense to me