Add support for using a managed identity to connect to Azure Database for PostgreSQL

[MattMcL4475]

To use managed identity:

1. In https://github.com/broadinstitute/cromwhelm/blob/main/coa-helm/templates/tes.yaml, set:

TesPostgreSql__DatabaseUserPassword=""
TesPostgreSql__UseManagedIdentity="true"

If UseManagedIdentity is true, an exception will be thrown if DatabaseUserPassword is NOT empty.

2. Enable "Microsoft Entra authentication" on the PostgreSQL database
3. Add a "Microsoft Entra Admin" and select the managed identity
4. Using the original admin, you must run:

GRANT ALL PRIVILEGES ON DATABASE tes_db TO "CLIENT_ID";
GRANT ALL PRIVILEGES ON ALL TABLES IN SCHEMA public TO "CLIENT_ID";
GRANT ALL PRIVILEGES ON SCHEMA public TO "CLIENT_ID";

Where CLIENT_ID is the user-assigned managed identity's client ID.

TODO: create the database with an Azure AAD admin user in the deployer, then create an AAD user
TODO: provide script for creating a new AAD user after creating the AAD admin and using that instead

Reference:

https://learn.microsoft.com/en-us/azure/postgresql/single-server/how-to-configure-sign-in-azure-ad-authentication
https://learn.microsoft.com/en-us/azure/postgresql/single-server/concepts-azure-ad-authentication
https://learn.microsoft.com/en-us/azure/postgresql/single-server/how-to-connect-with-managed-identity

#346