Allow background color for options

[okworx]

⚠️ 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 assign a background color for each option (or a group of them), because it improves readability for poll participants.

Describe possible solutions

In the admin view, each option could get a color picker to set the background fill color. When creating polls via the paste functionality where each line gets converted into an option, an optional prefix or suffix such as [[bgcolor #ffff00]] could be used.

Additional context

Let's consider a text poll with various options like this one:

To separate options that belong to the same context better visually, it would be wonderful if the background color for the option's description could be set individually per option, like this (mockup):