Auto-hide comments that only contain a label command

[Aaron1011]

When using the 'rustbot modify labels' command, the comment containing the command is essentially just noise. The GitHub UI already shows label changes in a more compact and readable format.

It would be useful for triagebot to auto-hide the comment containing the label command (assuming that the message has no other content).

According to isaacs/github#1480 (comment), this can be done through the GitHub GraphQL API.

[pietroalbini]

Oh, TIL you can hide comments from GraphQL while you can't from the REST API. We should probably implement auto-hiding in RLA as well!