Reduce number of GitHub requests if possible

[azerella]

This has come up before it seems in #140 😞

The max number of requests is 12,500 for any GitHub installation.

https://docs.github.com/en/developers/apps/building-github-apps/rate-limits-for-github-apps

We can't buy our way out of this it seems - we need to reduce the number of requests we process if possible or at least do better error handling

[TriplEight]

was mentioned in processbot and cicd matrix channels, also in paritytech/substrate#9934 (comment).
Processbot is a core thing in our processes. The primary goal here would be fixing the issue. We can't afford to either wait until the token is rotated or do this manually. And then, surely error handling is important.

As @gabreal mentioned, this is a way to monitor the usage.

Rate limiting is likely to happen only after the rush hour in our timezone, Shawn was posting the trouble after 21oo.

It might be due to that just a couple of days before JP started his vacation we've redeployed processbot with him. It used to be deployed by an initial developer so we couldn't look into the settings and token scope.

[azerella]

Turns out this issue was a false alarm, the issue is actually not related to rate limiting but simply an anomaly 404 issue.

I created #345 to track instead