bazel: Shift `proto_sync` to bazel (#21754)

Signed-off-by: Ryan Northey <ryan@synca.io>

Mirrored from https://github.com/envoyproxy/envoy @ 3dc0ad88e98851880922db88a04e640b5eb732a4

bazel/BUILD

@@ -2,6 +2,13 @@ load("@io_bazel_rules_go//proto:compiler.bzl", "go_proto_compiler")
 load("//:utils.bzl", "json_data")
 load(":repository_locations.bzl", "REPOSITORY_LOCATIONS_SPEC")
 load(":repository_locations_utils.bzl", "load_repository_locations_spec")
+load(
+    ":external_proto_deps.bzl",
+    "EXTERNAL_PROTO_CC_BAZEL_DEP_MAP",
+    "EXTERNAL_PROTO_GO_BAZEL_DEP_MAP",
+    "EXTERNAL_PROTO_IMPORT_BAZEL_DEP_MAP",
+    "EXTERNAL_PROTO_PY_BAZEL_DEP_MAP",
+)
 
 licenses(["notice"])  # Apache 2
 
@@ -23,3 +30,13 @@ json_data(
     name = "repository_locations",
     data = load_repository_locations_spec(REPOSITORY_LOCATIONS_SPEC),
 )
+
+json_data(
+    name = "external_proto_deps",
+    data = dict(
+        cc = EXTERNAL_PROTO_CC_BAZEL_DEP_MAP,
+        go = EXTERNAL_PROTO_GO_BAZEL_DEP_MAP,
+        imports = EXTERNAL_PROTO_IMPORT_BAZEL_DEP_MAP,
+        py = EXTERNAL_PROTO_PY_BAZEL_DEP_MAP,
+    ),
+)