feat(wfe-buildkit-protos): generate full BuildKit gRPC API (tonic 0.14)

New crate generating Rust gRPC stubs from the official BuildKit
proto files (git submodule from moby/buildkit). Control service,
LLB definitions, session protocols, and source policy.
tonic 0.14 / prost 0.14.

wfe-buildkit-protos/src/lib.rs

@@ -0,0 +1,19 @@
+//! Generated gRPC stubs for the full BuildKit API.
+//!
+//! Built from the official BuildKit proto files at
+//! <https://github.com/moby/buildkit>.
+//!
+//! ```rust,ignore
+//! use wfe_buildkit_protos::moby::buildkit::v1::control_client::ControlClient;
+//! use wfe_buildkit_protos::moby::buildkit::v1::StatusResponse;
+//! ```
+
+#![allow(clippy::all)]
+#![allow(warnings)]
+
+include!(concat!(env!("OUT_DIR"), "/mod.rs"));
+
+/// Re-export tonic and prost for downstream convenience.
+pub use prost;
+pub use prost_types;
+pub use tonic;