MySql: Support for Managed Identity Access

[Aniruddh25]

Need to add support for MySQL connection from the service using a ManagedIdentity.

Support for same has been already added for SQLDB:

Here are the docs:
https://github.com/Azure/data-api-builder/blob/main/docs/database-connections.md

Priority will be given to the credentials specified in the connection string. But if connection string doesn't specify UID or Password, an attempt is made to retrieve access token using DefaultAzureCredential. This will set the access token based on environment, or local dev scenario.

For the Phoenix hosted scenario, access token will be sent to the ConfigurationController and eventually to the RuntimeConfigProvider.Initialize call, See here: https://github.com/Azure/data-api-builder/blob/main/src/Service/Configurations/RuntimeConfigProvider.cs#L209
This is the access token that Static Web Apps will pass to Phoenix which will send to DAB.

See this PR for details on implementation for SQL: #784