ci: create stylelint workflow

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 6 lines in your changes are missing coverage. Please review.

Project coverage is 23.52%. Comparing base (6a5be67) to head (c59c4f2). Report is 2 commits behind head on main.

Files	Patch %	Lines
src/views/EditSidebar.vue	0.00%	3 Missing :warning:
.../AppNavigation/EditCalendarModal/SharingSearch.vue	0.00%	2 Missing :warning:
src/components/Shared/DatePicker.vue	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #5976 +/- ## ========================================= Coverage 23.52% 23.52% Complexity 455 455 ========================================= Files 246 246 Lines 11716 11716 Branches 2145 2154 +9 ========================================= Hits 2756 2756 + Misses 8646 8645 -1 - Partials 314 315 +1 ``` | [Flag](https://app.codecov.io/gh/nextcloud/calendar/pull/5976/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nextcloud) | Coverage Δ | | |---|---|---| | [javascript](https://app.codecov.io/gh/nextcloud/calendar/pull/5976/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nextcloud) | `15.16% <0.00%> (ø)` | | | [php](https://app.codecov.io/gh/nextcloud/calendar/pull/5976/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nextcloud) | `58.46% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nextcloud#carryforward-flags-in-the-pull-request-comment) to find out more.

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