feat(appointments): add timezone to all emails

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 23.48%. Comparing base (f7b0a99) to head (d30e6a7). Report is 5 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #6356 +/- ## ========================================= Coverage 23.47% 23.48% + Complexity 454 453 -1 ========================================= Files 247 247 Lines 11710 11716 +6 Branches 2224 2223 -1 ========================================= + Hits 2749 2751 +2 - Misses 8641 8645 +4 Partials 320 320 ``` | [Flag](https://app.codecov.io/gh/nextcloud/calendar/pull/6356/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/6356/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nextcloud) | `15.05% <ø> (ø)` | | | [php](https://app.codecov.io/gh/nextcloud/calendar/pull/6356/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nextcloud) | `59.35% <ø> (-0.08%)` | :arrow_down: | 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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