MPD media players are not listed in the dropdown

[ScotiaGranite]

On the configuration page the list of media players comes from the entity_registry which will not include entities which have no Unique_Id. This excludes the MPD media player because it is manually added via the configuration.yml so there is no way to target these players as the player_entity.

I can work around this by changing they type of input in the config_flow.py from this:

                ``vol.Optional("player_entity_id"): cv.multi_select(players),

to this:

                ``vol.Optional("player_entity_id"): str

This allows me to input the entity_name manually and the speaker now works for the alert noise as well as for the TTS output.