docs(ci): use up-to-date protoc with docs.rs

[wackywendell]

Which issue does this PR close?

Closes #13853.

Rationale for this change

This uses the same basic solution as in substrait-rs:

https://github.com/substrait-io/substrait-rs/blob/bbcc9f6d0b084a13706f39a43bbba9d37bf2a959/Cargo.toml#L62-L63

• substrait-rs has an optional protoc feature
  0 The protoc feature adds a dependency on protobuf-src, which ensures a fixed version of the protobuf compiler by compiling/vendoring it
• In the build.rs file, the vendored protoc is used when the protoc feature is enabled
• The feature is enabled for docs.rs

What changes are included in this PR?

Given that datafusion-substrait only uses the protoc compiler with the substrait-rs crate and already has a protoc feature, we should be able to solve this problem by enabling the protoc feature for docs.rs, as done here.

Are these changes tested?

This is difficult to test, as it depends on the docs.rs environment, which is hard to replicate.

I have verified locally that adding the same version of protoc to my path as in docs.rs leads to the problem, and is solved with enabling all features:

datafusion/datafusion/substrait ❯ PATH="$HOME/protobuf/bin:$PATH" cargo doc
…
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" }
datafusion/datafusion/substrait ❯ PATH="$HOME/protobuf/bin:$PATH" cargo doc --all-features
…
Documenting datafusion-substrait v44.0.0
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 1m 14s
   Generated /Users/wendell.smith/go/src/github.com/DataDog/datafusion/target/doc/datafusion_substrait/index.html

I have attempted to replicate this in a docs.rs environment following the instructions here and here, but running it on any local crate gives an error like invalid type: null, expected a string at line 1 column 2617950 and fails, so I haven't been able to do so.

Are there any user-facing changes?

No, other than that docs.rs should work again.

[alamb]

Thanks @wackywendell ❤️

I tested locally that building the docs with all features seems to work great:

$ cd datafusion/substrait/
$ cargo doc --all-features

Thank you for debugging this and your efforts to fix it ❤️

[alamb]

Thanks again @wackywendell