[CI] Buildkite for web emscripten build

Summary:
Add a build to check if properly generated .wasm files are committed to repo.

Depends on D8446

Test Plan:

1. Create new Buildkite pipeline: link.
2. Run new build and check if it passes: link to build.
3. Make some changes in CommQueryExecutor.cpp without generating new .wasm files, push it to branch and run new build, should fail: link to build.

Reviewers: michal, atul, jon, bartek

Reviewed By: atul, jon, bartek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8469