Enable AAD (Azure Active Directory) authentication

[KnicKnic]

I use Azure Managed Grafana and Azure Monitor workspace (promql endpoint).
I would like to use the MCP and have authentication be transparent in a system that has access to AAD auth.

What this would entail.

1. Establishing at startup the aad credential object
2. grabbing a token any time a call is about to be made
   1. recreating the http client associated with the token if the token is different from the previous time this was done
   2. This needs to done for both promql & grafana
3. updating the code to not proxy promql calls through grafana and send them direct
4. Adding some new type of config that would specify to do this

EDIT
Have submitted PR