Bug fix - wrong behaviour for should_create_index

[igiloh-pinecone]

Problem

The should_create_index was implemented like do_create_index instead of behaving like allow_existing_index, which is the original purpose.
When the user is setting should_create_index=False, he doesn't necessarily mean "don't create index", but rather "create index of you need to, but I allow upserting to existing one".

This behavior blocks other libraries that rely on pinecone-datasets to implicitly create the index if\when needed, like pinecone-context.

Solution

Altered the behavior to match intended design.

Type of Change

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

Test Plan

Already covered by existing tests