Allow redefine autodiscovery type

[brokenmass]

Unfortunately the previous PR (#4593 ) was incorrect as it was merging the type and object_id into the payload instead of the config.
This solves the issue by moving the type/object_id override logic to the right place, the getConfigs method

[Koenkk]

I'm wondering if exposing a switch as a light is the only use case for overriding. If that is the case I would prefer to rather introduce a switch for this. e.g.

devices:
  '0x12345678':
    friendly_name: my_switch
    homeassistant:
      switch_as_light: true

[brokenmass]

I don't think it's the only case. I can imagine it being used to configure switch as locks, or locks as switches, but yes it's a configuration that mostly affect switches (and other binary actuators).
I personally find a switch_as_light entry inside homeassistant a bit dirty as all the others values are overrides while that is a functionality toggle. Also it doesn't allow for multi-gang switches specific configuration (ie: 1 switch mapped as light the other left as switch)
The proposed solution instead allow for maximun configurability and it can be considered an advanced override, for people that want to control zigbee2mqtt exposed devices directly from z2m without using ha devices aliases.

[brokenmass]

@Koenkk : are you happy to merge this ?

[Koenkk]

yes, thanks! Also wrote some docs: https://github.com/Koenkk/zigbee2mqtt.io/blob/develop/docs/integration/home_assistant.md#exposing-switch-as-a-light