[basicprofiles] Add new "Flat Line" profile

[andrewfg]

Resolves #18291

Signed-off-by: Andrew Fiddian-Green [email protected]

[andrewfg]

@J-N-K I have an OH Core Architecture question in relation to this PR which you can perhaps answer.

The new FlatLineProfile class implements a periodic scheduled task on an external scheduled executor service. So when a FlatLineProfile instance is released it must inform that service to cancel that task. I did this by implementing AutoCloseable in FlatLineProfile and adding a @Deactivate method in the ProfileFactory component; this calls the respective close() method(s) when the component is unloaded.

I think this is OK for an addon such as this. However OH Core does have ProfileFactory components so I wonder if we need to do the same in those cases? => WDYT?