Display same-day pickups when signing into slots

What does this MR do?

Display same-day pickups when signing into slots

How confident are you it won't break things if deployed?

It's missing API tests right now, but won't break.

Links to related issues

Product team: [Mailvorschlag] Warnung bei zwei Abholungen zur gleichen Zeit ( Beta | Live )

Follow-up to !1825 (merged)

How to test

Create a few slots (some in different stores) and sign into them with one user. Confirm a few of them. Attempt to sign into another slot for that day.

You should see a list of scheduled pickups for that day, the confirmation state, and a link to the store. The list will load lazily. The button to finish joining should be disabled until this list has loaded.

Screenshots

Checklist

• TODO: API tests
• no unrelated changes
• asked someone for a code review
• set a "for:" label to indicate who will be affected by this change
• use "state:" labels to track this MR's state until it was beta tested
• added an entry to CHANGELOG.md
• add a short text that can be used in the release notes
• Once your MR has been merged, you are responsible to create a testing issue in Beta Testing Repo:
  • Consider writing a detailed description in German.
  • Describe in a few sentences, what should be tested from a user perspective.
  • Also mention different settings (e.g. different browsers, roles, ...). how this change can be tested.
  • Be aware, that also non technical people should understand.

Release notes text

(A short text that will appear in the release notes and describes the change for non-technical people. Not always necessary, e.g. not for refactoring.)