tag: set, add, remove tags

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 93.33333% with 3 lines in your changes missing coverage. Please review.

Project coverage is 81.68%. Comparing base (de439ee) to head (ae0e794). Report is 14 commits behind head on master.

Files with missing lines	Patch %	Lines
src/borg/archiver/tag_cmd.py	92.30%	1 Missing and 2 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #8449 +/- ## ========================================== + Coverage 81.64% 81.68% +0.03% ========================================== Files 71 72 +1 Lines 12906 12950 +44 Branches 2337 2345 +8 ========================================== + Hits 10537 10578 +41 - Misses 1707 1708 +1 - Partials 662 664 +2 ```

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