Integration config form: replace text inputs with entity lookup widgets

[davidecavestro]

Is your feature request related to a problem? Please describe.
As a user I don't like setting numeric IDs to relate sectors with arm mode (i.e. setting 2,3,4 on the areas_arm_home field and son on).

Describe the solution you'd like
I'd prefer selecting sectors from the list of available ones on my current system

Describe alternatives you've considered
Discussed on Discord.

Additional context

This is how it currently works

This is how I'd like to set it up (simulated using the Add group UI feature)

[palazzem]

When we work on this functionality, let's keep in consideration to include Alarm AWAY configuration (related to: #96)

[palazzem]

@xtimmy86x assigning this to you!