Add maintenance status endpoint

[valyo]

Before submitting this PR

1. Description: Adds get method to maintenance endpoint
2. Jira task / GitHub issue: DDS-1436, DDS-1651
3. How to test: Test together with https://github.com/ScilifelabDataCentre/dds_cli/pull/644
4. Type of change: Check the relevant boxes in the section below
5. Add docstrings and comments to code, even if you personally think it's obvious.

What type of change(s) does the PR contain?

• [ ] New feature
  • [ ] Breaking: Please describe the reason for the break and how we can fix it.
  • [x] Non-breaking
• [ ] Database change
  • [ ] Migration included in PR
  • [ ] Migration not needed
• [ ] Bug fix
  • [ ] Breaking: Please describe the reason for the break and how we can fix it.
  • [ ] Non-breaking
• [ ] Security Alert fix
• [ ] Documentation
• [ ] Tests (only)
• [ ] Workflow

Checklist

• Sprintlog
  • [x] Added
  • [ ] Not needed (E.g. PR contains only tests)
• Rebase / Update / Merge from base branch (the branch from which the current is forked)
  • [x] Done
  • [ ] Not needed
• Blocking PRs
  • [ ] Merged
  • [x] No blocking PRs
• PR to master branch
  • [ ] Yes: Read the release instructions
  • [ ] I have followed steps 1-8.
  • [x] No

Actions / Scans

• Black: Python code formatter. Does not execute. Only tests. Run black . locally to execute formatting.
  • [x] Passed
• Prettier: General code formatter. Our use case: MD and yaml mainly. Run npx prettier --write . locally to execute formatting.
  • [x] Passed
• Yamllint: Linting of yaml files.
  • [x] Passed
• Tests: Pytest to verify that functionality works as expected.
  • [x] New tests added
  • [ ] No new tests
  • [x] Passed
• CodeQL: Scan for security vulnerabilities, bugs, errors
  • [ ] New alerts: Go through them and either fix, dismiss och ignore. Add reasoning in items below.
  • [ ] Alerts fixed: What?
  • [ ] Alerts ignored / dismissed: Why?
  • [x] Passed
• Trivy: Security scanner
  • [ ] New alerts: Go through them and either fix, dismiss och ignore. Add reasoning in items below.
  • [ ] Alerts fixed: What?
  • [ ] Alerts ignored / dismissed: Why?
  • [x] Passed
• Snyk: Security scanner
  • [ ] New alerts: Go through them and either fix, dismiss och ignore. Add reasoning in items below.
  • [ ] Alerts fixed: What?
  • [ ] Alerts ignored / dismissed: Why?
  • [x] Passed

[codecov[bot]]

Codecov Report

Merging #1459 (a67e251) into dev (abb196e) will increase coverage by 0.01%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              dev    #1459      +/-   ##
==========================================
+ Coverage   89.49%   89.51%   +0.01%     
==========================================
  Files          29       29              
  Lines        4390     4396       +6     
==========================================
+ Hits         3929     3935       +6     
  Misses        461      461              

Files Changed	Coverage Δ
dds_web/api/__init__.py	100.00% <100.00%> (ø)
dds_web/api/superadmin_only.py	98.82% <100.00%> (+0.04%)	:arrow_up: