grpcio builds from source

[devoxel]

This is because the alpine docker does nothing to prevent "manywheels" installations, which cause grpcio to build from source.

See grpc#11125 and pip#3969.

We have a few options for fixing:

• As Ross pointed out, we could create an image for heavier building dependencies, and inherit from that
• We could disable manywheels (we probably still should), so that we don't build from source

Thought filing an issue would let us track this better.

[devoxel]

We could alternatively properly layer our builds (by putting dependencies related to each consumer on separate lines) or use multi-stage builds

Multi stage is probably a little over-engineering, docker will cache each line of the Dockerfile if the line doesn't change. If a line towards the top of the list changes, then all layers beneath are rebuilt.

[CianLR]

I think the idea of sticking grpcio as one of the first lines is decent, everyone goes through it once but it's cached from then on.

I'm not familiar with manywheels though, if disabling that is an easy fix then perhaps that's we should do.