pw_protobuf: Add Bazel plugin targets and deps

Adds bazel target for the python protoc plugin and includes
com_google_protobuf as a WORKSPACE dependency.

Change-Id: I346474fe8ddf7fec16b7e433596426bba50ba2ff
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/15321
Reviewed-by: Akira Baruah <akirabaruah@google.com>
Reviewed-by: Keir Mierle <keir@google.com>
Commit-Queue: Akira Baruah <akirabaruah@google.com>
diff --git a/WORKSPACE b/WORKSPACE
index 6aa2053..9c25067 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -53,6 +53,22 @@
 
 protobuf_deps()
 
+# Setup tools to build custom grpc rules.
+# Regquired by: pigweed.
+# Used in modules: //pw_protobuf
+http_archive(
+    name = "rules_proto_grpc",
+    sha256 = "5f0f2fc0199810c65a2de148a52ba0aff14d631d4e8202f41aff6a9d590a471b",
+    strip_prefix = "rules_proto_grpc-1.0.2",
+    urls = ["https://github.com/rules-proto-grpc/rules_proto_grpc/archive/1.0.2.tar.gz"],
+)
+
+load("@rules_proto_grpc//:repositories.bzl", "rules_proto_grpc_repos", "rules_proto_grpc_toolchains")
+
+rules_proto_grpc_toolchains()
+
+rules_proto_grpc_repos()
+
 # Set up build_bazel_rules_nodejs.
 # Required by: pigweed.
 # Used in modules: //pw_web_ui.
@@ -88,11 +104,14 @@
 
 npm_bazel_karma_dependencies()
 
-load(
-    "@io_bazel_rules_webtesting//web:repositories.bzl",
-    "web_test_repositories",
+http_archive(
+    name = "io_bazel_rules_webtesting",
+    sha256 = "9bb461d5ef08e850025480bab185fd269242d4e533bca75bfb748001ceb343c3",
+    urls = ["https://github.com/bazelbuild/rules_webtesting/releases/download/0.3.3/rules_webtesting.tar.gz"],
 )
 
+load("@io_bazel_rules_webtesting//web:repositories.bzl", "web_test_repositories")
+
 web_test_repositories()
 
 load(