Support any patch version of protobuf 3.19 (#172)

## Problem

> Describe the purpose of this change. What problem is being solved and
why?

The very precise specifier `protobuf==3.19.3` doesn't allow for security
updates, or any flexibility within the patch version.

At the time of writing, the `google-api-core` PyPI package
[uses](https://github.com/googleapis/python-api-core/blob/v2.11.0/setup.py#L33)
a specifier of `>=3.19.5`, making these two significant packages
incompatible with each other.

## Solution

> Describe the approach you took. Link to any relevant bugs, issues,
docs, or other resources.

Allow `3.19.*` but no less than `3.19.3`.

This change would allow Pinecone's client to be installed alongside the
[PaLM API client
library](https://github.com/google/generative-ai-python).


## 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)
- [x] Non-code change (docs, etc)
- [ ] None of the above: (explain here)

## Test Plan

> Describe specific steps for validating this change.

I'm hoping your CI will validate this 🤞

Co-authored-by: Gareth <[email protected]>
Co-authored-by: Jennifer Hamon <[email protected]>

Author: 3 people

requirements-grpc.txt

@@ -2,4 +2,4 @@ grpcio>=1.44.0
 grpc-gateway-protoc-gen-openapiv2==0.1.0
 googleapis-common-protos>=1.53.0
 lz4>=3.1.3
-protobuf==3.19.5
+protobuf~=3.19.5