Validate that the vector storage setup is correct

Problem/Motivation

For example the following checks are not made when saving configuration

1. text-embedding-ada-002 requires 1536 dimensions
2. openai API key must be set

Steps to reproduce

Start a fresh openai_embeddings project, create pinecone index with different dimensions, miss setting openai key.

Proposed resolution

Add validation.

Remaining tasks

Add validation.

User interface changes

Embeddings setting validates configuration.

API changes

None.

Data model changes

None.