fix(appointments): log calculated start and end times for slot generation

[codecov[bot]]

Codecov Report

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

Project coverage is 23.60%. Comparing base (9196525) to head (13ad251). Report is 4 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #6051 +/- ## ============================================ + Coverage 23.59% 23.60% +0.01% Complexity 457 457 ============================================ Files 246 246 Lines 11714 11716 +2 Branches 2140 2150 +10 ============================================ + Hits 2764 2766 +2 + Misses 8636 8635 -1 - Partials 314 315 +1 ``` | [Flag](https://app.codecov.io/gh/nextcloud/calendar/pull/6051/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/6051/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nextcloud) | `15.18% <ø> (ø)` | | | [php](https://app.codecov.io/gh/nextcloud/calendar/pull/6051/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nextcloud) | `58.65% <ø> (+0.03%)` | :arrow_up: | 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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[miaulalala]

/backport to stable4.7