bot, plugin, plugin.rules: optionally include admins in rate limits too

[dgw]

Description

Implementation of my own idea from #2435, an optional include_admins kwarg to @plugin.rate and related decorators.

With #2647 settled, I can now open this and (hopefully) not run into any unrelated CI fails.

Checklist

• I have read CONTRIBUTING.md
• I can and do license this contribution under the EFLv2
• No issues are reported by make qa (runs make lint and make test)
  • It passed locally when I was working on the patch. Haven't rerun things on top of the current master branch, but the lazy way is letting CI do it for me.
• I have tested the functionality of the things this change touches