[EPIC] Darkmode for discussion

[alinaboghiu]

Ensure Discussion components are compatible with dark mode.

Please refer to this Figma file with details for the tweaks. The task list crashes when I start adding tasks it so I won't rely on it for detailed stuff.

### Tasks
- [ ] https://github.com/guardian/dotcom-rendering/issues/10701
- [ ] https://github.com/guardian/dotcom-rendering/issues/10716
- [ ] https://github.com/guardian/dotcom-rendering/issues/10718
- [ ] https://github.com/guardian/dotcom-rendering/issues/10717
- [ ] https://github.com/guardian/dotcom-rendering/issues/10765
- [ ] 06__Comment top when someone is replying to another comment: tweaks to alignment — See Figma file for details
- [ ] 07__Text links everywhere: add underlining — See Figma file for details
- [ ] https://github.com/guardian/dotcom-rendering/issues/10739
- [ ] 09__Text formatting tools: styling tweaks — See Figma file for details
- [ ] 10__Text formatting tools: change position on mobile breakpoints — See Figma file for details
- [ ] 11__Pre-moderation warning: use 'Info Summary' from Source instead — See Figma file for details
- [x] https://github.com/guardian/dotcom-rendering/issues/10754
- [ ] https://github.com/guardian/dotcom-rendering/issues/10744

[shesah]

@benwuersching are you currently working on this?

[cemms1]

Storybook link is here to check dark mode compatibility for Discussion components. Searching for "discussion" in the left hand panel makes it easier to find the discussion-related components

[cemms1]

Chromatic build link here https://www.chromatic.com/build?appId=63e251470cfbe61776b0ef19&number=6762

@benwuersching is going to review the Storybook link and these changes and then suggest some improvements for the dark mode designs

[cemms1]

Have split out the preliminary work to add basic dark mode compatibility to Discussion components from this ticket and converted this to an epic ticket to detail the design optimisations for dark mode components