Create /api/search/random

[Difegue]

This API should take search filters and categories in order to be able to pull a random entry from a given search/category.
Ideally, it should also have a number, so we can pull 1, 5 or 10+ random archives in one call.

/api/search/random?category=xxxxx&filter=yyyy&count=5

[Difegue]

Documentation for the new endpoint can be found at the usual spot: https://sugoi.gitbook.io/lanraragi/v/dev/api-documentation/search-api#get-random-archives-out-of-the-index.