Implement fixed age intervals

[MaHaWo]

first version (obsolete)

• done in preparation to the statistics computation things in the feedback backend
• no fixed milestone timedelta anymore (that we had set to 6 months), but a configurable interval per milestone
• backend endpoints for adding, removing and modifying age intervals
  • I'm not entirely sure if allowing modification is a good idea as it will invalidate previous analysis/feedbacks
• milestones have an new ageinterval member that tells to which interval they belong.
  • there would be the possibility to compute this interval automatically if the data is good enough, but I'm not sure we can do this reliably, and would prefer if they would do that on their side of things and then just put in the numbers instead of giving us some algorithm for it that we have to implement and maintain and be responsible for
• new tab in admin frontend interface for the age intervals
• new element in the milestone frontend to select it.
• adjusted the database query that pulls out the relevant answers for the milestoneanswersession based on time.
• vast majority of the indicated changes come from the regenerated openapi.json file.

revised version

• new elements expected_age_months_minus and expected_age_months_plus in milestone database models.
• these are relative to expected_age_months
• adjusted the database query that pulls out the relevant answers for the milestoneanswersession based on time.
• age interval for a milestone = [expected_age_months-expected_age_months_minus, expected_age_months + expected_age_months_plus]
• add three-way range slider frontend component and replace the slider for expected_age_months in EditMiletoneModal with that to edit the age interval for a milestone in one go.
  • styling was surprisingly difficult to get consistent between firefox and chromium, and it's still a bit off :(

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 10.52632% with 68 lines in your changes missing coverage. Please review.

Project coverage is 29.71%. Comparing base (78c1a9e) to head (236639c).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
...src/lib/components/Admin/EditMilestoneModal.svelte	0.00%	32 Missing ⚠️
...nd/src/lib/components/DataInput/RangeSlider.svelte	0.00%	24 Missing and 1 partial ⚠️
frontend/src/lib/components/MilestoneGroup.svelte	0.00%	9 Missing ⚠️
...nd/src/lib/components/Admin/MilestoneGroups.svelte	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #194      +/-   ##
==========================================
- Coverage   30.16%   29.71%   -0.46%     
==========================================
  Files         103      106       +3     
  Lines        3388     3507     +119     
  Branches       91       94       +3     
==========================================
+ Hits         1022     1042      +20     
- Misses       2290     2386      +96     
- Partials       76       79       +3     

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[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

[MaHaWo]

@lkeegan will we use this thing now or should it be closed (will keep the branch around locally though in that case)

[lkeegan]

I guess it's all implemented in other PRs by now? So yes, let's close the PR but keep the branch in case

[MaHaWo]

no, it's not. in fact, I went to some lengths to not pollute other PRs with this....