feat: add shortcuts to other instances

[AkesiSeli]

Technical details

This PR adds the possibility to configure "shortcuts" to other instances to be able to see contents there and interact with them.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 93.93939% with 4 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...in/content/repository/DefaultTimelineRepository.kt	89.47%	1 Missing and 3 partials ⚠️

Flag	Coverage Δ
unittests	62.39% <93.93%> (+1.91%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...coonforfriendica/navigation/DefaultDetailOpener.kt	89.50% <100.00%> (+0.23%)	⬆️
...accoonforfriendica/core/navigation/DetailOpener.kt	100.00% <ø> (ø)
...ent/pagination/DefaultTimelinePaginationManager.kt	66.81% <100.00%> (+0.58%)	⬆️
...ca/domain/content/repository/TimelineRepository.kt	22.22% <100.00%> (+22.22%)	⬆️
...ty/repository/DefaultInstanceShortcutRepository.kt	100.00% <100.00%> (ø)
...in/content/repository/DefaultTimelineRepository.kt	71.69% <89.47%> (+71.69%)	⬆️

... and 1 file with indirect coverage changes