Spring-ai Updated several vector db docs to fix errors and to expand on instructions for successful outcomes

Fixed several documentation bugs across the following vector DBs: - Postgres/PGvector - Neo4j - Azure AI Search

Added required properties/code samples to successfully implement Neo4j as a VectorStore. These were missing.

Other docs fixes as appropriate.

Comment From: mkheck

Good morning, @tzolov, please let me know if you need anything else. Cheers!

Comment From: tzolov

Merged! Thanks @mkheck