feat: parallelize event overview api requests

[abhinavk96]

Reduces event overview page load time significantly, removes redundant promise for event details, as ember resolves models hierarchically, it's already resolved before the hook is called.

Fix for #4099

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[codecov]

Codecov Report

Merging #4406 into development will decrease coverage by 0.10%.
The diff coverage is 0.00%.

@@               Coverage Diff               @@
##           development    #4406      +/-   ##
===============================================
- Coverage        22.68%   22.58%   -0.11%     
===============================================
  Files              468      468              
  Lines             4950     4960      +10     
  Branches             6        6              
===============================================
- Hits              1123     1120       -3     
- Misses            3826     3839      +13     
  Partials             1        1              

Impacted Files	Coverage Δ
app/routes/events/view/index.js	0.00% <0.00%> (ø)
app/components/tabbed-navigation.js	33.33% <0.00%> (-20.00%)	⬇️

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[abhinavk96]

@iamareebjamal allSettled is crashing the page. Checking, why.

[iamareebjamal]

https://github.com/fossasia/open-event-frontend/pull/4400/files#diff-ca71ae366a21b955d046c55d41739777R48