Migrate codebase to TypeScript

[QazCetelic]

No major changes have been made aside from adding types. All 4 added dependencies are development dependencies. These consist of types (@types/jest, @types/react, @types/react-dom) and jiti (required for using TS for config files).

There are still parts that miss proper types, I think this will require writing interfaces for all API responses. I can look into that later, if desired.

[QazCetelic]

I forgot to format the code with prettier, this has been done now.

[QazCetelic]

Linking https://github.com/kopia/kopia/issues/2096

[jkowalski]

@QazCetelic this still has conflicts, could you look into that?

[jkowalski]

btw, the plan is to cut the release without this change, so that we can start next version with merging this PR