Implement container provisioner gRPC client

[yulmwu]

For details about the Container Provisioner gRPC server, refer to the PR below:

• Add gRPC server, Protobuf setup, and CI publish workflows container-provisioner-k8s#14

In this PR, a client has been implemented based on the gRPC proto, and environment variables have been added to allow toggling between HTTP and gRPC communication. The added environment variables are as follows:

STACKS_PROVISIONER_USE_GRPC=false
STACKS_PROVISIONER_GRPC_ADDR=localhost:9090
# STACKS_PROVISIONER_API_KEY is shared.

The Proto IDL is also managed using Buf Schema Registry (BSR).

make buf-install
buf registry login

make buf-generate

Existing stubs are located under internal/gen/stack/v1.

[yulmwu]

This PR does not meet the test coverage target (>= 70%).

[Copilot]

Pull request overview

Implements a gRPC-based client for the Container Provisioner and adds configuration switches to select between the existing HTTP client and the new gRPC client at runtime.

Changes:

• Add internal/stack gRPC client implementation and generated protobuf stubs under internal/gen/stack/v1.
• Extend stack configuration/env to support STACKS_PROVISIONER_USE_GRPC and STACKS_PROVISIONER_GRPC_ADDR, and wire selection logic in the server entrypoint.
• Add Buf/BSR generation tooling (Makefile + buf.gen.yaml) and update examples/docs.

Reviewed changes

Copilot reviewed 11 out of 16 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
README.md	Documents new env vars and Buf/BSR workflow (currently has a formatting issue inside the env code block).
Makefile	Adds targets for buf install/lint/generate plus basic Go fmt/vet/test/build.
internal/stack/grpc_client.go	New gRPC client implementation for StackService (timeout and transport security need follow-ups).
internal/http/integration/testenv_test.go	Minor formatting alignment in test config literals.
internal/http/integration/admin_test.go	Minor formatting alignment in test config literals.
internal/http/handlers/testenv_test.go	Minor formatting alignment in test config literals.
internal/gen/stack/v1/stack.pb.go	Generated protobuf messages/enums for StackService API.
internal/gen/stack/v1/stack_grpc.pb.go	Generated gRPC client/server interfaces and handlers for StackService.
internal/config/config.go	Adds stack gRPC address/enable flags; validates base URL vs gRPC addr based on mode; includes in log formatting.
go.mod	Adds grpc/protobuf dependencies and updates indirect deps accordingly.
go.sum	Updates dependency checksums due to grpc/protobuf/buf-related dependency graph changes.
codecov.yaml	Excludes new gRPC client file from coverage (consistent with existing HTTP client exclusion).
cmd/server/main.go	Selects HTTP vs gRPC provisioner client based on config and initializes the chosen implementation.
buf.lock	Adds Buf lockfile metadata.
buf.gen.yaml	Configures Buf code generation plugins/paths for Go and Go gRPC.
.env.example	Adds the new stack gRPC toggle/address environment variables.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.