Add API endpoints for planned maintenance tasks

[johannaengland]

Scope and purpose

Fixes #1774.

Potential follow up issue: Make it possible to filter on the GET endpoint.

Contributor Checklist

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• Added a changelog fragment for towncrier
• Added/amended tests for new/changed code
• Added/changed documentation, including updates to the user manual if feature flow or UI is considerably changed
• Linted/formatted the code with ruff and djLint, easiest by using pre-commit
• The first line of the commit message continues the sentence "If applied, this commit will ...", starts with a capital letter, does not end with punctuation and is 50 characters or less long. See our how-to
• If applicable: Created new issues if this PR does not fix the issue completely/there is further work to be done
• If this results in changes in the UI: Added screenshots of the before and after
• If this results in changes to the database model: Updated the ER diagram

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

Test results

    8 files  1 728 suites   3m 11s ⏱️
  958 tests   957 ✅ 1 💤 0 ❌
7 664 runs  7 656 ✅ 8 💤 0 ❌

Results for commit aabe02b.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.75%. Comparing base (8a3dcda) to head (aabe02b).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1930      +/-   ##
==========================================
+ Coverage   88.60%   88.75%   +0.14%     
==========================================
  Files         146      149       +3     
  Lines        7093     7149      +56     
==========================================
+ Hits         6285     6345      +60     
+ Misses        808      804       -4     

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