feat: add jenkins plugin downloader

[PierreSchwang]

Adds a kinda-easy & standardized way to download Jenkins artifacts instead of doing all the rest calls and delegating to url() in the projects itself.

Haven't used Kotlin that much (as most likely visible) - so open for review and modifications ^^

(Ignore the branch name...)

[jpenilla]

The API requests should be cached similarly to how the Modrinth metadata is. The other thing is the cache doesn't handle changing versions currently. We should add some sort of marker and have a configuration for how often to refresh them.

[PierreSchwang]

The API requests should be cached similarly to how the Modrinth metadata is. The other thing is the cache doesn't handle changing versions currently. We should add some sort of marker and have a configuration for how often to refresh them.

I don't think Jenkins provides any kind of E-Tag header or anything remotely similar nor useful there. I just downloaded the remote jar and didn't care about potential duplicated builds as that should never happen either way (as it's incrementing and therefor kinda cache-controlled).

The only thing that could be cached would be the latest build-number - but that would either require an appropriate response header (which feels way over the top as the response body is literally a few bytes) or some kind of duration for cache hits (which might impact UX)