Add a field in config to disable/enable the string hashing in metric report.

Statsd hashes (using its own hashing function) raw strings to reduce the
upload data size when there are duplicate strings in the report. And in cloud,
the clearcut translator would backfill the strings.

In a few droidfood users, we find the translator was unable to do that. While
debugging the root cause, we first decided to provide an option to disable
the hashing from the cloud.

Test: statsd unit test, CTS test, tested manually

BUG: b/79943763
Change-Id: If0359c8cf3f3cf83a2938db9ebf95ea7906f0b0c