RGB(W) MQTT integration change

[klew]

After adding RGBW commands support (#280) please change MQTT integration in following way:

1. Add separate state values for RGB and Dimmer parts as state/rgb/on and state/dimmer/on. Common "state/on" may be left as it is.
2. Add separate topic for execute_action for RGB and Dimmer parts: "~/execute_action/rgb" and "~/execute_action/dimmer". Common topic "~/execute_action" may stay as it is.

Additionally change "on_cmd_type" to "last".

Changes should be done for RGBW, RGB, and Dimmer - when flag SUPLA_CHANNEL_FLAG_RGBW_COMMANDS_SUPPORTED is set.

Here is example of HA discovery for RGB part (used on device's local MQTT integration):

{
   "avty_t":"supla/devices/rgbw-device-01-0a1618/state/connected",
   "pl_avail":"true",
   "pl_not_avail":"false",
   "~":"supla/devices/rgbw-device-01-0a1618/channels/0",
   "dev":{
      "ids":"rgbw-device-01-0a1618",
      "mf":"Test",
      "name":"RGBW device 01",
      "sw":"23.10-debug.01"
   },
   "name":"RGB Lighting",
   "uniq_id":"supla_08b61f0a1618_0_1",
   "qos":0,
   "ret":false,
   "opt":false,
   "stat_t":"~/state/rgb/on",
   "cmd_t":"~/execute_action/rgb",
   "pl_on":"TURN_ON",
   "pl_off":"TURN_OFF",
   "stat_val_tpl":"{% if value == \"true\" %}TURN_ON{% else %}TURN_OFF{% endif %}",
   "on_cmd_type":"last",
   "bri_cmd_t":"~/set/color_brightness",
   "bri_scl":100,
   "bri_stat_t":"~/state/color_brightness",
   "rgb_stat_t":"~/state/color",
   "rgb_cmd_t":"~/set/color"
}

and here is a dimmer part:

{
   "avty_t":"supla/devices/rgbw-device-01-0a1618/state/connected",
   "pl_avail":"true",
   "pl_not_avail":"false",
   "~":"supla/devices/rgbw-device-01-0a1618/channels/0",
   "dev":{
      "ids":"rgbw-device-01-0a1618",
      "mf":"Test",
      "name":"RGBW device 01",
      "sw":"23.10-debug.01"
   },
   "name":"Dimmer",
   "uniq_id":"supla_08b61f0a1618_0_0",
   "qos":0,
   "ret":false,
   "opt":false,
   "stat_t":"~/state/dimmer/on",
   "cmd_t":"~/execute_action/dimmer",
   "pl_on":"TURN_ON",
   "pl_off":"TURN_OFF",
   "stat_val_tpl":"{% if value == \"true\" %}TURN_ON{% else %}TURN_OFF{% endif %}",
   "on_cmd_type":"last",
   "bri_cmd_t":"~/set/brightness",
   "bri_scl":100,
   "bri_stat_t":"~/state/brightness"
}