[Database Migration] Update CLI scripts to work with PostgreSQL

[Enniwhere]

Description:
PostgreSQL and pgvector does not provide built-in functionality for creating and updating vector indexes nor for keeping track of vector index metadata, so we need to migrate this functionality as well.

Acceptance criteria:

• Keep and update the following:
• • create_vector_index.py
• • update_vector_indexes.py
• • populate_vector_index_metadata.py (may be migrated into create_vector_index.py)
• Remove the following:
• • create_fts_index.py
• • create_openai_embedding_batches.py
• • add_batch_embeddings_to_index.py

Technical details:
Optional technical details for context.