ENH: use happi audit for auto-generated PRs

We now have an happi audit, which we could integrate with the diff tool (#45)

Perhaps running happi audit only on the changed / added devices is enough?  

Ignoring the connection test seems prudent, since devices can go up and down.  An instantiation check might be sufficient here (along with all the metadata checks)

I can add a full happi audit cron job as well, somewhat 