wasm: add gRPC tests written using Proxy-Wasm Rust SDK.

[PiotrSikora]

Fixes #16432.

Signed-off-by: Piotr Sikora piotrsikora@google.com

[repokitteh-read-only]

CC @envoyproxy/dependency-shepherds: Your approval is needed for changes made to (bazel/.*repos.*\.bzl)|(bazel/dependency_imports\.bzl)|(api/bazel/.*\.bzl)|(.*/requirements\.txt)|(.*\.patch).

🐱

Caused by: #16722 was opened by PiotrSikora.

see: more, trace.

[PiotrSikora]

(Blocked on #16430)

[moderation]

This two changes to the existing bazel/repository_locations.bzl Rust Rules and Rust SDK look OK, but this PR brings in additional Rust dependencies via Cargo (I think just protobuf). /cc @htuch to chime in on the extent to which we want to actively maintain and manage dependencies in the Rust / WASM space

[moderation]

/lgtm deps

[htuch]

/lgtm deps

I think it's fine to have Rust fetched independently as long as this isn't in the core and is confined to tests. Ideally we would have the Rust deps in as few places as possible, this is going to be bazel/external/cargo?

[PiotrSikora]

I think it's fine to have Rust fetched independently as long as this isn't in the core and is confined to tests.

Yes, this is only for tests.

Ideally we would have the Rust deps in as few places as possible, this is going to be bazel/external/cargo?

Correct, and we need this only for Rust deps that are not used in the Rust SDK, since we don't have BUILD rules for them.