Populating/Updating dropdown roller btnmatrix items at runtime (after HA connected)

[nagyrobi]

Use cases:

• display light's effect_list attribute
• media player's source_list and sound_mode_list
• any select options import from HA

Items for dropdown roller and btnmatrix are natively added to the widgets with a string where \n is the delimiter.

For example importing the sound_mode_list attribute of media_player.my_room into an ESPHome text sensor with filters:

text_sensor:
  - platform: homeassistant
    name: "Media Player sound modes"
    id: mplaymodes
    entity_id: media_player.my_room
    attribute: sound_mode_list
    filters:
      - substitute:
        - "', '-> \\n"
        - "[ -> "
        - "] -> "
        - "' -> "

results in:
Classic\nJazz\nNormal\nPop\nVocal
which can be used to directly populate a dropdown roller or a btnmatrix with these items.

Suggestion for dropdown roller and btnmatrix would be to have a config option like text_items which could accept strings like above mutually exclusive with buttons >text or symbol sub-options. The other styling options could still be possible per item.

With lvgl.widget.update this could be updated at runtime.

Also in pair with #40

Use case for the example above is with on_value the user could call a HA service to choose the desired sound mode (we need the selected item name in a variable, see #49 (comment))