chore: drop usage of jquery in install and update interfaces

[SychO9]

Fixes #3457

Changes proposed in this pull request:

• Just converts the JS code to vanilla JS.
• Tesed locally.

Necessity

• Has the problem that is being solved here been clearly explained?
• If applicable, have various options for solving this problem been considered?
• For core PRs, does this need to be in core, or could it be in an extension?
• Are we willing to maintain this for years / potentially forever?

Confirmed

• Frontend changes: tested on a local Flarum installation.
• Backend changes: tests are green (run composer test).
• Core developer confirmed locally this works as intended.
• Tests have been added, or are not appropriate here.

Required changes:

• Related documentation PR: (Remove if irrelevant)
• Related core extension PRs: (Remove if irrelevant)

[askvortsov1]

https://stackoverflow.com/a/37401912 might be a better fit, actually

[SychO9]

let me just switch back to jQuery 🤣

[askvortsov1]

Aaaaaaaaa noooooo!!!!!!!

[matteocontrini]

A bit late here, but I think fetch Promise rejections should be handled too. Otherwise network errors are ignored (they weren't, in the previous jQuery implementation).