Update authentication in Azure Data Explorer datasource

[kostrse]

Work involved to migrate the plugin authentication to external module github.com/grafana/grafana-azure-sdk-go and make it in line with other Azure datasources.

• Migrate client secret auth to Grafana Azure SDK #358
• MSAL for On-Behalf-Of token requests #372
• Azure settings should be received from the Grafana host #357
• Update backend to common AzureCredentials #360
• Update frontend to common Azure Authentication UI and AzureCredentials format #361
• All requests should use user identity auth if user identity configured #509
• Enable Managed Identity authentication in Azure Data Explorer datasource #362
• CurrentUserContext to carry current user identity to the authentication layer #525
• Configurable Azure authentication middleware for support of custom token providers grafana-azure-sdk-go#16
• On-behalf-of token provider using configurable middleware #542