Expose future stub on Pinecone connection

[russcam]

This commit exposes the future stub on Pinecone connection, allowing for non-blocking async calls

Problem

PineconeConnection does not currently expose a stub for making asynchronous calls to the service. Async calls are very common in high traffic services.

Solution

Exposed the generated VectorServiceGrpc.VectorServiceFutureStub on PineconeConnection. This returns com.google.common.util.concurrent.ListenableFuture<V> for each call, which allows chaining of asynchronous operations.

The PR also removes an unused public method, setBlockingStub; can add this back if client API compatibility dictates.

Type of Change

• 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

Run sanityAsyncFuture test

[rohanshah18]

@russcam Thanks for making the changes for async stub. I was successfully able to run the integration tests locally against your changes. I have left a comment for reverting the test file changes since I'm in plans of rewriting them. Once reverted, I'll approve your PR and we can merge the changes!!

[russcam]

I've reverted the test changes @rohanshah18

[rohanshah18]

Looks good to me, thanks for reverting the test changes!