feat(theme): add theme variables option

[piitaya]

Description

Allow theme override for each mushroom card.

TODO : add the option on all cards

type: custom:mushroom-entity-card
entity: switch.decorative_lights
theme_variables:
  rgb-state-entity: var(--rgb-green)
  rgb-disabled: var(--rgb-red)

Like others options, the option is available from UI

Related Issue

Nop

Motivation and Context

Advanced users want to customize their card. For now, they use card_mod. This PR allow to override mushroom variables without using card_mod and from the UI.

How Has This Been Tested

Types of changes

• [ ] 🐛 Bug fix (non-breaking change which fixes an issue)
• [x] 🚀 New feature (non-breaking change which adds functionality)
• [ ] 🌎 Translation (addition or update a translation)
• [ ] ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• [x] My code follows the code style of this project.
• [x] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] I have tested the change locally.

[ulic75]

Is there something in particular blocking this PR beside the documentation update? I don't have a lot of free time and am about to go on vacation, but I could lend a hand perhaps. This seems like a really nice feature.

Oh, probably waiting for the shared config stuff to get finished up, that makes sense.

[piitaya]

I'm working on a huge refactoring because maintaining lot of duplicate code is complicated 😅 https://github.com/piitaya/lovelace-mushroom/pull/528

I prefer to finish it before provide new big feature 🙂

[soeffi]

Do I understand correctly, that this feature has never made it into the code-base? Just wondering why this was closed, as it seems to be a nice addition - for me especially with respect to the cover card, as I run into the same issues as discussed in #384 ...