Auto tag authorities that have received no/very few requests

[FOIMonkey]

Similar to the auto tagging of missing emails, this would enable us to suggest users make requests to these authorities and/or offer suggestions as to what they could ask for.

[FOIMonkey]

Related to #7362

[garethrees]

Yep, this was pretty trivial https://github.com/mysociety/alaveteli/pull/7363.

A couple of questions:

1. What counts as "very few"? I've gone with "under 5". Feels about right?
2. What do we want the tag to be called. I've gone with not_many_requests, but it's an easy change if we can think of something a bit better.
3. I've ignored the fact there may be 100s of currently-private requests. Do we want the tag applied if that's still the case, or do we only want it applied where there are very few requests total (rather than very few currently public requests)?

[FOIMonkey]

1. I think less than 5 makes sense for now, we can always up it later.
2. not_many_requests is perfect.
3. I'm fine ignoring embargoed requests. The chances of there being tons made to a tiny parish meeting somewhere is negligible, and it keep the appearance of any note consistent with what the average user/visitor can see.

[WilliamWDTK]

I'd agree with only counting public (non-embargoed, non-reduced-prominence) requests, such that the presence of the note is consistent with the body's public page.

Regarding number, do we have means/medians/etc for the number of public requests to bodies with which this could be compared?

[garethrees]

Potential source of good questions https://clairemiller.net/blog/2013/01/a-great-big-list-of-foi-ideas/

[garethrees]

FDS have a great list of suggested requests based on authority category https://fragdenstaat.de/hilfe/erste-anfrage/anfrage-ideen/