Documentation for the PostgreSQL vector store connector (#204)

* Add Postgres connector code samples

* Update postgres connector docs.

Includes some expanded docs around dotnet and adds docs for the python

* Address link feedback from leran-build-service-prod

* Remove reference of KernelBuilder extension

* Add example of connection string

* Fix client name

* Fix generics

* Update create table statement

* Fix missing using in example

* Fix dotnet entra auth

* dotnet doc small fix

* Add vector index section

* Fix incorrect Python examples

* python: Improve data mapping section

* formatting

* dotnet: fix var name

* Give example of entra conn str

* dotnet: Update CREATE TABLE

* Fix mention of named vectors

* Refactor Postgres connector imports and update data model annotations

* Update dotnet PostgreSQL connector docs based on feedback.

* Fix example for ensure_collection_exists rename

Author: lossyrob

semantic-kernel/concepts/vector-store-connectors/code-samples.md

@@ -50,6 +50,7 @@ vector store they create to use with the common code.
 
 - [Azure AI Search vector search with common code](https://github.com/microsoft/semantic-kernel/blob/main/dotnet/samples/Concepts/Memory/VectorStore_VectorSearch_MultiStore_AzureAISearch.cs)
 - [InMemory vector search with common code](https://github.com/microsoft/semantic-kernel/blob/main/dotnet/samples/Concepts/Memory/VectorStore_VectorSearch_MultiStore_InMemory.cs)
+- [Postgres vector search with common code](https://github.com/microsoft/semantic-kernel/blob/main/dotnet/samples/Concepts/Memory/VectorStore_VectorSearch_MultiStore_Postgres.cs)
 - [Qdrant vector search with common code](https://github.com/microsoft/semantic-kernel/blob/main/dotnet/samples/Concepts/Memory/VectorStore_VectorSearch_MultiStore_Qdrant.cs)
 - [Redis vector search with common code](https://github.com/microsoft/semantic-kernel/blob/main/dotnet/samples/Concepts/Memory/VectorStore_VectorSearch_MultiStore_Redis.cs)