Add gRPC service definition for ACR<->ADP IPC

Restore the AcrIpc gRPC service with four RPCs:
 - Handshake (unary)
 - SendCheckData (unary with ACK)
 - SendCheckResult (unary)
 - StreamConfig (server streaming for config push).

 Re-enable server and client codegen for the checks proto compilation.

Author: nathan-b

lib/protos/datadog/build.rs

@@ -146,8 +146,8 @@ fn main() {
         .expect("Failed to build gRPC service definitions for Datadog Agent.");
 
     tonic_prost_build::configure()
-        .build_server(false)
-        .build_client(false)
+        .build_server(true)
+        .build_client(true)
         .include_file("checks.mod.rs")
         .compile_protos(
             &[

lib/protos/datadog/proto/checks/v1/acr_ipc.proto

@@ -71,3 +71,22 @@ message CheckResultMsg {
   string check_id = 3;
   string error = 4;
 }
+
+// Trivial request/response types for RPCs that don't need a body.
+message StreamConfigRequest {}
+message SendCheckResultResponse {}
+
+// gRPC service for ACR <-> ADP IPC.
+service AcrIpc {
+  // Handshake — first call after connecting.
+  rpc Handshake(Hello) returns (HelloResp);
+
+  // Check data submission with acknowledgement.
+  rpc SendCheckData(CheckDataMsg) returns (CheckDataAck);
+
+  // Check result reporting.
+  rpc SendCheckResult(CheckResultMsg) returns (SendCheckResultResponse);
+
+  // Server pushes config updates to the client as a stream.
+  rpc StreamConfig(StreamConfigRequest) returns (stream ConfigData);
+}