Move API resource pbs to new location (#1484)

This moves the generated pb files to the `sdk` module. This allows third parties to make use of them if desired (e.g. in upcoming plugins) and moves away from the `gen` nomenclature in the directory, since we are going to be adding some extra interface functions to the messages.

internal/gen/controller/api/services/user_service.pb.go

@@ -8,7 +8,7 @@ package services
 
 import (
 	_ "github.com/grpc-ecosystem/grpc-gateway/v2/protoc-gen-openapiv2/options"
-	users "github.com/hashicorp/boundary/internal/gen/controller/api/resources/users"
+	users "github.com/hashicorp/boundary/sdk/pbs/controller/api/resources/users"
 	_ "google.golang.org/genproto/googleapis/api/annotations"
 	protoreflect "google.golang.org/protobuf/reflect/protoreflect"
 	protoimpl "google.golang.org/protobuf/runtime/protoimpl"