Enhancements for the markdown editor

[HelNershingThapa]

Tracking anticipated enhancements for the markdown text editor here:

• [x] Add support to upload image by selecting an image with a button on the toolbar (https://github.com/hotosm/tasking-manager/pull/5386#issuecomment-1286011769)
• [ ] [BUG] Default list is not shown when @ button is clicked on the toolbar
• [ ] Include support to add YouTube videos from the toolbar
• [x] Add support for spell check [from Slack]
• [x] Disable dark mode feature
• [ ] https://github.com/hotosm/tasking-manager/issues/5460
• [x] #5491

[martien-176]

@HelNershingThapa, doesn't the addition of a preview tab to the editor also belong to this list?

[HelNershingThapa]

@martien-176 If you're talking about the editor in other sections besides the one mentioned in this pull request https://github.com/hotosm/tasking-manager/pull/5386, then it doesn't belong here. This editor differs from the ones found in the project edit sections. We'll indeed migrate the same editor to those sections in the coming months; thank you for your patience.

[dakotabenjamin]

There is a bug while using the #author tag accidentally stylizing when it's the first text of the line:

https://hotosm.slack.com/archives/C319P09PB/p1696963590721069