Update frontend to common Azure Authentication UI and AzureCredentials format

[kostrse]

Azure datasources have common design and implementation of configuration UI, common schema of AzureCredentials in JsonData and common implementation of parsers. This facilitates code reuse, easier changes across the board and consistency in user experience.

One of the features which are supported by other Azure datasources but not by Azure Data Explorer is Managed Identity (MSI) authentication.

As a precondition for implementation of MSI authentication, the Azure authentication section of configuration UI should be replaced by same implementation from other Azure datasources and credentials schema should be updated to same schema used by other datasources.

Here is the code which could be borrowed from Prometheus datasource.

Directory: /public/app/plugins/datasource/prometheus/configuration

• AzureCredentialsForm.tsx - React component for Azure authentication configuration section
• AzureAuthSettings.tsx#L20-L26 - example of usage of AzureCredentialsForm
• AzureCredentials.ts - domain objects, definitions of AzureCredentials
• AzureCredentialsConfig.ts - reading/writing of AzureCredentials from/to JsonData

Since ADX has existing credentials format, extra logic should be implemented which would read credentials in old format if credentials in new format were not found, so they would be rewritten in new format when saved.

This requires backend implementation first:

• Update backend to common AzureCredentials #360