After some discussion, we decided to change the DSL to get rid of
the `plist_name` and `service_name` methods which aren't meaningful
for most users.
The new DSL looks like this:
```rb
service do
name macos: "name", linux: "name"
end
```
I also updated some specs here to reflect these changes.
There was some talk about maybe deprecating `plist_name` and `service_name`
but I think that's outside of the scope of this PR so I'm leaving
them as is for now. One benefit of this is that everything here is backwards
compatible.