Upgrade to grpc 1.0 (grpc_server) and test against Envoy 1.38.2 in CI

[larshesel]

This PR contains two changes (see commits):

1. Upgrade to grpc 1.0 via grpc_server
2. Also test against Envoy 1.38.2 in CI

---

1. Upgrade to grpc 1.0 via grpc_server

Migrates ex_control_plane to grpc 1.0.0, which split the previously monolithic grpc package into three:

• grpc_core — shared base (GRPC.Service, GRPC.Credential, …)
• grpc — client (GRPC.Stub, …)
• grpc_server — server implementation (GRPC.Server, GRPC.Endpoint, GRPC.Server.Stream, interceptors, supervisor)

Since ex_control_plane is a gRPC server (xDS/ADS), it now depends on grpc_server ~> 1.0 instead of pulling grpc transitively via envoy_xds.

Why this works

The package split preserved all public module namespaces. Every gRPC module this project uses still exists under the same name, just sourced from grpc_server:

• GRPC.Server.Supervisor (application.ex)
• use GRPC.Server (aggregated_discovery_service_server.ex)
• GRPC.Server.Stream.send_reply/3 (stream.ex)
• use GRPC.Endpoint + GRPC.Server.Interceptors.Logger (endpoint.ex)

As a result no source changes are required — this is a dependency-only change.

Motivation — security

grpc 0.11.x is affected by four advisories fixed only in grpc 1.0.0, including a 9.2 Critical (RCE/DoS via unsafe Erlang term deserialization). Staying on 0.11.x left every consumer of ex_control_plane transitively exposed. Upgrading also drops gun from the dependency tree entirely (it becomes an optional dep of the grpc client only), removing three further gun advisories.

envoy_xds dependency

envoy_xds now tracks the latest upstream proxyconf/envoy_xds_ex main, which carries the matching grpc ~> 1.0 / protobuf ~> 0.17 bump and a refreshed xDS proto set (merged via proxyconf/envoy_xds_ex#7):

{:envoy_xds, git: "https://github.com/proxyconf/envoy_xds_ex.git"},

An earlier revision of this PR temporarily pointed at a fork branch while that bump was in review; it now points back at upstream.

2. Also test against Envoy 1.38.2 in CI

Adds Envoy 1.38.2 (current stable) to the CI test matrix alongside the existing 1.37.0 and 1.36.4, so the integration tests run against the latest Envoy minor in addition to the two prior ones:

# Envoy stable (1.38) and the two prior minors (1.37, 1.36)
envoy: ["1.38.2", "1.37.0", "1.36.4"]

How this was tested

Verified with Elixir 1.19 / OTP 28:

• Dependency resolution (rm mix.lock && mix deps.get): resolves grpc_server 1.0.0, grpc 1.0.0, grpc_core 1.0.0, protobuf 0.17.0; gun is not resolved into the tree.
• Compile: mix compile --warnings-as-errors succeeds with no source changes; zero redefining module warnings.
• Tests: full suite passes — 75 tests, 0 failures, 1 skipped (1 doctest). The gRPC ADS/CDS/LDS streams are exercised end-to-end.
• Envoy 1.38.2: ran the envoy integration suite (9 tests) and the full suite (75 tests) against the Envoy 1.38.2 release binary — 0 failures.