build(deps,ci): add protoc feature to build protoc from source

[wackywendell]

Fixes #355, by using the same setup for protoc as substrait-io/substrait-rs.

Testing

I checked locally:

1. Download [email protected] from here, to get the same version as is used in the docs.rs workspace (ubuntu 22.04).
2. Run PATH="/path/to/downloaded/protobuf/bin:$PATH" cargo doc

• Shows me the error Error: Custom { kind: Other, error: "protoc failed: substrait/algebra.proto: This file contains proto3 optional fields, but --experimental_allow_proto3_optional was not set.\n" }, as seen in the docs.rs build

3. Run PATH="/path/to/downloaded/protobuf/bin:$PATH" cargo doc --features protoc, to see it succeed

So this shows that it uses protobuf-src correctly. I haven't been able to confirm that the docs.rs metadata works correctly; I haven't been able to reproduce this inside a docs.rs docker container.

[wackywendell]

I'm also going to see if I can add some CI for this feature once I open the PR, which should validate / ensure that the protoc feature continues to build hermetically. I'll move it from draft to 'Ready for Review' once that seems to work; in the meantime, having a draft PR means that the CI will run.

[wackywendell]

OK, tests pass, this should be ready to review!

[mbrobbel]

Thanks!

[westonpace]

This is very nice, thank you!

[wackywendell]

Thanks, @EpsilonPrime, @mbrobbel and @westonpace!