Add theme support to media control card

[spacegaier]

Proposed change

Technically themes were already supported, but the card editor did not show it plus the card preview did not take it into account (no dynamic updating).

Note: Many other tweaks (e.g. spelling of other conf properties) to this page are part of this PR against current: #16281

Type of change

• Spelling, grammar or other readability improvements (current branch).
• Adjusted missing or incorrect information in the current documentation (current branch).
• Added documentation for a new integration I'm adding to Home Assistant (next branch).
  • I've opened up a PR to add logo's and icons in Brands repository.
• Added documentation for a new feature I'm adding to Home Assistant (next branch).
• Removed stale or deprecated documentation.

Additional information

• Link to parent pull request in the codebase: Allow themeing of media control card frontend#8209
• Link to parent pull request in the Brands repository:
• This PR fixes or closes issue:

Checklist

• This PR uses the correct branch, based on one of the following:
  • I made a change to the existing documentation and used the current branch.
  • I made a change that is related to an upcoming version of Home Assistant and used the next branch.
• The documentation follows the Home Assistant documentation standards.

[frenck]

✅ Approved. Can be merged as soon as the parent PR gets merged.