Allow Markdown formatting for options

⚠️ 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 format the description of options in Markdown syntax, because it improves readability for poll participants.

Describe possible solutions

Similar to the description of the poll itself, which already accepts Markdown syntax, the same could be applied to the description of the individual options.

In addition, being able to add line breaks e.g. by inserting a \n would be super helpful, too.

Additional context

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

To make things better readable, it would be great if a portion of the option's description could be formatted bold, like this (mockup):

Being able to add line breaks to the individual descriptions would add even more flexibility.

The issue names no files or tests. Start by locating the existing Markdown handling for poll descriptions and the rendering entry point for individual option descriptions; compare their behavior, including line breaks. Done means option descriptions support the requested Markdown formatting and line breaks in the participant view.