Add towncrier to produce changelog

[johannaengland]

To avoid merge conflicts on direct changes to CHANGELOG.md for every PR.

Also adds towncrier to pre-commit and Github Actions.

[github-actions[bot]]

Test results

    3 files      3 suites   47s :stopwatch: 315 tests 315 :heavy_check_mark: 0 :zzz: 0 :x: 945 runs  943 :heavy_check_mark: 2 :zzz: 0 :x:

Results for commit 4bf374ec.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 98.97%. Comparing base (bae714c) to head (4bf374e). Report is 6 commits behind head on master.

:exclamation: Current head 4bf374e differs from pull request most recent head 4325485

Please upload reports for the commit 4325485 to get more accurate results.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #220 +/- ## ========================================== - Coverage 98.98% 98.97% -0.00% ========================================== Files 49 47 -2 Lines 6558 6532 -26 ========================================== - Hits 6491 6465 -26 Misses 67 67 ```

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[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud