[dashboard] Update theme preference selector

[gtsiolis]

Problem to solve

The first part of the dark theme has been added in #3901. However, we are still missing a better styled theme selector.

Theme Selector

Proposal

We could:

1. Update the theme selector style to follow the design language of the rest of the product and make the option more appealing to the user. This could use something like the card component used above in the editor preference.
2. Default to light theme to be less surprising to the user. Preference order could be Light, Dark, System.
3. Update the section design description to something more descriptive or maybe playful like Early bird or night owl? Choose your side.
4. Consider introducing a secondary option to sync theme between dashboard and editor, see [dashboard] Sync theme preference between dashboard and editor #3982 (comment).

Designs

Light	Dark

See also design specs.

[jankeromnes]

Looks awesome! ✨ Many thanks @gtsiolis. 🙏

Additional thought: Once implemented, it could be nice to just copy/paste this Theme switcher into the "What's New" modal (thus allowing users to switch the Theme directly from What's New). Thoughts? 😇

[gtsiolis]

Absolutely @jankeromnes! That was the plan, similarly to what @AlexTugarev did with the account select process in #3897. But haven't thought this through yet in terms of how this design will scale but it should could be fine. Will cross-check and post any updates in #3956. 🤷