Add DIR_METADATA file to components/local_state dir.

This powers the chrome://local-state page, which was added as a
debugging tool to inspect the contents of the Local State file,
which is primarily used to support metrics and variations.
Using the same DIR_METADATA file as components/variations.

Bug: 1371826
Change-Id: I4007b55c88f0e43595c0b31544b25305807ca648
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3938666
Commit-Queue: Alexei Svitkine <asvitkine@chromium.org>
Reviewed-by: Luc Nguyen <lucnguyen@google.com>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1059416}

components/local_state/DIR_METADATA

@@ -0,0 +1,5 @@
+monorail {
+  component: "Internals>Metrics>Variations"
+}
+
+team_email: "chromium-dev@chromium.org"