FI-2405: Create skeleton loader for main app

[AlyssaWang]

Summary

Adds skeleton loading components to the test session portion of Inferno. Follow up tickets will implement skeletons for the landing page and suite options page.

Testing Guidance

Skeletons should appear while portions of the application are loading. Please let me know if they aren't doing so!

[codecov]

Codecov Report

Attention: 58 lines in your changes are missing coverage. Please review.

Comparison is base (58320f3) 77.09% compared to head (39d4f80) 77.32%.

Files	Patch %	Lines
...nt/src/components/TestSuite/TestSessionWrapper.tsx	30.23%	30 Missing ⚠️
client/src/components/Skeletons/FooterSkeleton.tsx	83.67%	2 Missing and 6 partials ⚠️
client/src/components/Skeletons/HeaderSkeleton.tsx	86.04%	1 Missing and 5 partials ⚠️
client/src/components/Skeletons/DrawerSkeleton.tsx	89.13%	1 Missing and 4 partials ⚠️
...t/src/components/Skeletons/TestSessionSkeleton.tsx	92.42%	1 Missing and 4 partials ⚠️
client/src/components/Skeletons/AppSkeleton.tsx	90.62%	0 Missing and 3 partials ⚠️
client/src/components/Header/Header.tsx	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #440      +/-   ##
==========================================
+ Coverage   77.09%   77.32%   +0.22%     
==========================================
  Files         220      225       +5     
  Lines       10951    11200     +249     
  Branches     1030     1052      +22     
==========================================
+ Hits         8443     8660     +217     
- Misses       1929     1939      +10     
- Partials      579      601      +22     

Flag	Coverage Δ
backend	93.92% <ø> (ø)
frontend	70.15% <79.43%> (+0.55%)	⬆️

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[arscan]

Huge improvement! I tried it out with our demo suites, and also g10 after running the full suite of single patient api tests, which causes the interface load time to be a bit long right now. A todo for us is to optimize some of our db calls to improve load time, but this is a nice short term measure for that, plus being noticeably better in the regular case.

My only concern here is that it would add enough complexity and/or maintenance effort when we update the look and feel to make it simply not worthwhile to put in. But in looking through the code, it looks like there are very few spots in the 'real' interface that link over to this skeleton (so, low complexity), and the skeleton API seems really simple to update (so, low enough maintenance cost for if/when we update the UI). So I definitely think its worthwhile.

I'm not so concerned about skeletons on the landing/suites part of the UI, as that has a decent likelyhood of being refactored down the road as we consider backporting jekyll updates we made to inferno.healthit.gov into the test kit template.

[arscan]

I did see a bit of a flicker for suites with options due to some kind of reloading going on, which might be a little more annoying now that this page isn't just a grey blob, but I think we are aware of that issue.