Create method in Index class for fetching IDs of all vectors in index

[Tylersuard]

Problem

Pinecone does not have any way for users to fetch all IDs of all vectors in an index.

Solution

Loop and query until the number of unique IDs matches the number of vectors in the index.

Type of Change

• [ X] Bug fix (non-breaking change which fixes an issue)
• [ X] New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [X ] This change requires a documentation update
• Infrastructure change (CI configs, etc)
• Non-code change (docs, etc)
• None of the above: (explain here)

Test Plan

Try it.

[Tylersuard]

@rajat08 @benjaminran

[daverigby]

Note that v3.1 has introduced the list and list_pagnated API methods (Serverless only) which use a server-side implementation which should be significantly quicker than the brute-force search approach used above.