Markdown support

[nickvergessen]

• Overview ticket: Basic text formatting to chat spreed#1027
• API discussion: Markdown support - API spreed#9950

We plan to role out the following support for markdown:

non-optional

• bold
• italic

optional

Optional means it is just shown with the markdown syntax

• strike-through
• list
• todo list with checkboxes
• code block using 3 `
• inline code using `
• quote
• headlines
• dividers ---

[nickvergessen]

I'm aware of #3154 just created a new ticket for tracking until we know whether we want to have an option for markdown on/off

[AndyScherzinger]

@nickvergessen I checked the formatting list and ticket all boxes since the Android implementation supports all of them. Also adding an option to disable this completely should be very easy to do, only disabling parts is unlikely to work given the nature of the library in use.

[nickvergessen]

There is a markdown property on messages now. If that is false, all Markdown rendering should be disabled:
nextcloud/spreed#10067