NOISSUE - Allow interoperability with CC Attestation Agent (#568)

* feat: Add Confidential Containers attestation agent as an alternative attestation backend with new proto definitions and build system integration.

Signed-off-by: Sammy Oina <sammyoina@gmail.com>

* fix: Update protoc-gen-go and protoc-gen-go-grpc versions in CI workflow

Signed-off-by: Sammy Oina <sammyoina@gmail.com>

* feat: Add mock implementation for AttestationAgentServiceClient and corresponding tests

Signed-off-by: Sammy Oina <sammyoina@gmail.com>

* fix: Add missing periods to test function comments in provider_test.go

Signed-off-by: Sammy Oina <sammyoina@gmail.com>

---------

Signed-off-by: Sammy Oina <sammyoina@gmail.com>

agent/cvms/cvms_grpc.pb.go

@@ -3,7 +3,7 @@
 
 // Code generated by protoc-gen-go-grpc. DO NOT EDIT.
 // versions:
-// - protoc-gen-go-grpc v1.5.1
+// - protoc-gen-go-grpc v1.6.0
 // - protoc             v6.33.1
 // source: agent/cvms/cvms.proto
 
@@ -69,7 +69,7 @@ type ServiceServer interface {
 type UnimplementedServiceServer struct{}
 
 func (UnimplementedServiceServer) Process(grpc.BidiStreamingServer[ClientStreamMessage, ServerStreamMessage]) error {
-	return status.Errorf(codes.Unimplemented, "method Process not implemented")
+	return status.Error(codes.Unimplemented, "method Process not implemented")
 }
 func (UnimplementedServiceServer) mustEmbedUnimplementedServiceServer() {}
 func (UnimplementedServiceServer) testEmbeddedByValue()                 {}
@@ -82,7 +82,7 @@ type UnsafeServiceServer interface {
 }
 
 func RegisterServiceServer(s grpc.ServiceRegistrar, srv ServiceServer) {
-	// If the following call pancis, it indicates UnimplementedServiceServer was
+	// If the following call panics, it indicates UnimplementedServiceServer was
 	// embedded by pointer and is nil.  This will cause panics if an
 	// unimplemented method is ever invoked, so we test this at initialization
 	// time to prevent it from happening at runtime later due to I/O.