[ProjectSchedule] Add read-only variant, typing, tests

[imnasnainaec]

Closes #707

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This change is 

[codecov-commenter]

Codecov Report

Patch coverage: 13.33% and project coverage change: +0.25% 🎉

Comparison is base (9ffd0a8) 67.70% compared to head (25ae15b) 67.95%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2414      +/-   ##
==========================================
+ Coverage   67.70%   67.95%   +0.25%     
==========================================
  Files         240      240              
  Lines        8254     8247       -7     
  Branches      504      505       +1     
==========================================
+ Hits         5588     5604      +16     
+ Misses       2308     2287      -21     
+ Partials      358      356       -2     

Flag	Coverage Δ
backend	79.61% <ø> (-0.07%)	⬇️
frontend	54.35% <13.33%> (+0.59%)	⬆️

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Files Changed	Coverage Δ
...ojectSettings/ProjectSchedule/DateScheduleEdit.tsx	0.00% <0.00%> (ø)
...s/ProjectSettings/ProjectSchedule/DateSelector.tsx	0.00% <0.00%> (ø)
...rojectSettings/ProjectSchedule/ProjectSchedule.tsx	46.15% <0.00%> (+46.15%)	⬆️
src/components/ProjectSettings/index.tsx	69.56% <ø> (ø)
...s/ProjectSettings/ProjectSchedule/CalendarView.tsx	41.17% <66.66%> (+41.17%)	⬆️

... and 1 file with indirect coverage changes

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[jasonleenaylor]

Reviewed 8 of 9 files at r1, 1 of 1 files at r2, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @imnasnainaec)