Python: Add Azure DB for PostgreSQL vector store

[lossyrob]

Motivation and Context

This adds a VectorStore for Azure DB for PostgreSQL.

Currently, the only additional functionality this provides over the PostgresVectorStore is to easily connect to the database using Entra authentication. In the future, we will add capability to leverage the new DiskANN indexing.

Description

• Leverage the ability to pass in a custom AsyncConnection class to psycopg_pool's AsyncConnectionPool. The custom AsyncEntraConnection class will identify if a azure.core.credentials TokenCredential or AsyncTokenCredential has been passed as a 'credential' connection argument, or supply the DefaultAzureCredentials if no user or password has been set. This will be used to set the username and password for the Entra user for each new connection the pool creates.
• The AzureDBForPosgresSettings overrides methods from PostgresSettings to provide Entra authentication, allowing the user and password to not be set and generating the connection pool with AsyncEntraConnection
• The tutorial was updated to allow the user to choose either AzureDBForPostgres or Postgres as the vector store.

TODO:

• Unit tests
• Integration tests

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄

[markwallace-microsoft]

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
2659	4 💤	0 ❌	0 🔥	1m 22s ⏱️