Rename package to `connectrpc`

A few things to consider:

• Package name on pypi: connectrpc, this will translate to pip install connectrpc
• src/connect -> src/connectrpc, this will affect how the package is imported and used, import connectrpc.
• What does the repository name become under the connectrpc org? connectrpc/connectrpc-python? This feels kinda bad?
• Name for the protoc generator, current is protoc-gen-connect-python and honestly, this feels good. Would it become something like protoc-gen-connectrpc-python ?

I'm questioning the value of naming the package connectrpc over being connect-python.

cc @akshayjshah