Parallelize more work

[ebidel]

In lighthouse-data.mjs there are opportunities to parallelize some of the promises in saveReport. We touch memcache, firestore several times, and cloudstorage to update metadata, cache entries, and (re-save) reports.

We could push some of these onto an array and use await Promise.all().

I'll explore this once https://github.com/GoogleChrome/lighthouse-keeper/pull/10/files is in. Want to benchmark it too :)