feat: caldav push sync poc

[st3iny]

TODO:

• Authentication?
• Backend implementation (in server)
• Move registering code to some js library (to share it with other apps)

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 41 lines in your changes missing coverage. Please review.

Project coverage is 23.46%. Comparing base (0ae73bc) to head (b34d696).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
src/services/pushService.js	0.00%	37 Missing and 4 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #6348      +/-   ##
============================================
- Coverage     23.73%   23.46%   -0.28%     
  Complexity      454      454              
============================================
  Files           247      248       +1     
  Lines         11729    11742      +13     
  Branches       2213     2206       -7     
============================================
- Hits           2784     2755      -29     
- Misses         8625     8663      +38     
- Partials        320      324       +4     

Flag	Coverage Δ
javascript	15.01% <0.00%> (-0.33%)	⬇️
php	59.53% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.