Support date-only poll options

[andreas1107]

⚠️ This issue respects the following points: ⚠️

• I agree to follow Nextcloud's Code of Conduct.

Describe the goal you'd like to achieve

As a poll owner, I want to be able to suggest date-only options (without timing) because it allows for flexible scheduling, e.g. agreeing to meet in the evening on a certain date without agreeing to the exact time.

This was requested earlier here: #2290

Many thanks for a great product!!

Describe possible solutions

No response

Additional context

The issue today is that an all day event is displayed as bridging two different dates, which is confusing, because it looks like a two-day event is proposed. I hope the attached screenshots of poll visitor (first screenshot) and poll creator (second screenshot) display how unintuitive this is currently.

[andreas1107]

I believe the following issue is also related: #2368