Implement extended maintainer search/filtering

[AMDmi3]

After repology/repology-updater#539 was implemented, maintainers list page begs for extended search/filtering similar to what we have for projects. The usecase could be to see maintainer list along with activity statistics for a given repository.

As suggested by @juippis in repology/repology-updater#925, this can also solve the problem (exaplined in repology/repology-updater#539 (comment)) of picking the most representative repository for a maintainer.

The minimal goal is thus to support filtering maintainers by repository. This would likely require additional repository_maintainers SQL table, however such table would also help to implement #54.

Another needed feature is allowing maintainers list pagination in all cases (e.g. search and filtering).

[acxz]

Could searching/sorting maintainers by list of number of packages they maintain also be added? Or would this be a separate issue?

[AMDmi3]

What's the usecase?

[acxz]

Not too exactly sure what the usecase would be besides comparing maintainers, but it would be nice to have a sorting feature for maintainers (# projects, most active repo, etc) similar to the sorting feature for repositories.

[AMDmi3]

Repository sorting is free and straightforward as they fit on a single page, but with maintainers it would involve extra development and technical cost (indexes, more complex pagination), and doesn't have much sense on global maintainers view as different entities are mixed there (real maintainers, ehich may have different meaning among different repositories, maintainer groups, real and generated pseudomaintainers, CPAN accounts, github accounts etc). May make more sense on a per-repository maintainer lists though, but we don't have such thing yet.

[acxz]

I see, whoa that seems much more complicated than I thought it would be. Just wanted to express interest in a sort feature for maintainers but I understand if it involves a lot work for minimal gains. Thank you for responding back to me!
Keep on doing the great work!!