Audit use of ForceRocksDBCompactInTest and rename

Jira Link: DB-1508 Despite this methods name, we seem to have used this method in void TabletServiceAdminImpl::FlushTablets

void Tablet::ForceRocksDBCompactInTest() {
  if (regular_db_) {
    docdb::ForceRocksDBCompact(regular_db_.get());
  }
  if (intents_db_) {
    CHECK_OK(intents_db_->Flush(rocksdb::FlushOptions()));
    docdb::ForceRocksDBCompact(intents_db_.get());
  }
}

One obvious issue with this method in production code is the use of CHECK_OK. This only affects admin CLI flush commands, so this isn't a huge deal, but we should fix this regardless and ensure there are no other obvious or subtle issues with using this in production

cc @spolitov