feat: added settings endpoints

[ErikBjare]

Replaces https://github.com/ActivityWatch/aw-server/pull/84

aw-server-rust changes to unify the API: https://github.com/ActivityWatch/aw-server-rust/pull/428

[codecov[bot]]

Codecov Report

Attention: 23 lines in your changes are missing coverage. Please review.

Comparison is base (90c8b30) 55.64% compared to head (d5e64c9) 55.39%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #147 +/- ## ========================================== - Coverage 55.64% 55.39% -0.26% ========================================== Files 11 12 +1 Lines 629 677 +48 ========================================== + Hits 350 375 +25 - Misses 279 302 +23 ``` | [Files](https://app.codecov.io/gh/ActivityWatch/aw-server/pull/147?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ActivityWatch) | Coverage Δ | | |---|---|---| | [aw\_server/api.py](https://app.codecov.io/gh/ActivityWatch/aw-server/pull/147?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ActivityWatch#diff-YXdfc2VydmVyL2FwaS5weQ==) | `58.33% <57.14%> (-0.06%)` | :arrow_down: | | [aw\_server/rest.py](https://app.codecov.io/gh/ActivityWatch/aw-server/pull/147?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ActivityWatch#diff-YXdfc2VydmVyL3Jlc3QucHk=) | `67.72% <45.45%> (-1.18%)` | :arrow_down: | | [aw\_server/settings.py](https://app.codecov.io/gh/ActivityWatch/aw-server/pull/147?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ActivityWatch#diff-YXdfc2VydmVyL3NldHRpbmdzLnB5) | `53.33% <53.33%> (ø)` | |

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