Restructure repo for multiple client languages

[jhamon]

Problem

Need to reorganize some things to make way for other language clients.

Solution

• Create a new clients/ directory to hold each client we build around the rust library.
• Create a clients/python directory to be the new home of everything related to the python client
  • Move pinecone => clients/python
  • Move tests/unit => clients/python/tests/unit
  • Rename the python cargo package from pinecone to pinecone_python_client to reflect the fact it is the python client.
  • After changing the cargo package name, I needed to add a pyo3 annotation to specify the name of the compiled python module. We previously were relying on some default behavior.
  • Update all CI configs and makefiles to reflect these new code locations and package names

Type of Change

• [x] None of the above: Refactoring.

Test Plan

See cargo build and maturin develop succeed.