feat(webcal): Thunderbird holiday subscription picker

[ChristophWurst]

For #962

Todo

• Design work
• Subscribe handling

[codecov]

Codecov Report

Patch coverage: 5.74% and project coverage change: -0.16 ⚠️

Comparison is base (5f071dd) 22.58% compared to head (2687af3) 22.42%.

❗ Current head 2687af3 differs from pull request most recent head 1de6116. Consider uploading reports for the commit 1de6116 to get more accurate results

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #5167      +/-   ##
============================================
- Coverage     22.58%   22.42%   -0.16%     
  Complexity      373      373              
============================================
  Files           236      237       +1     
  Lines         11480    11570      +90     
  Branches       2152     2174      +22     
============================================
+ Hits           2593     2595       +2     
- Misses         8887     8975      +88     

Flag	Coverage Δ
javascript	13.90% <5.74%> (-0.12%)	⬇️
php	63.92% <ø> (ø)

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Impacted Files	Coverage Δ
...nts/AppNavigation/CalendarList/CalendarListNew.vue	0.00% <0.00%> (ø)
...ponents/Subscription/HolidaySubscriptionPicker.vue	0.00% <0.00%> (ø)
src/store/calendars.js	0.00% <0.00%> (ø)
src/services/caldavService.js	31.74% <31.25%> (+0.16%)	⬆️

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[JohannesGGE]

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