Refinements to entity references

[zoe-codez]

Changes

Upgrades to entities so that they better reflect what the service is asking for

• the multiple flag is now respected
• if no domain is listed, type will default to PICK_ENTITY instead of string

Observed changes in my setup

Service	Affected parameters	Before -> After
group.set	add_entities, entities, remove_entities	string -> PICK_ENTITY[]
logbook.log	entity_id	string -> PICK_ENTITY
media_player.join	group_members	always array now
scene.create	snapshot_entities	string -> PICK_ENTITY[]

Checklist

• Read the contribution guide and accept the
  code of conduct
• Readme and docs (updated or not needed)
• Tests (added, updated or not needed)