Tweak BridgeDB metrics file names.

We were using the same path for BridgeDB metrics in out/ and recent/,
and file names didn't contain the "-bridgedb-metrics" suffix that we
intended to add.

We're now using paths generated by BridgedbMetricsPersistence.

Also update create-tarballs.sh to create BridgeDB metrics tarballs.

Still part of #19332.