Add 'max devices' config to Energy Devices Graph

[thomaskonrad]

Proposed change

I'd like to propose adding an optional max_devices config setting to the Devices Energy Graph. If the setting is present, the card will only list the top N devices instead of all devices.

The use case is that users might want to only show the N biggest energy consumers in their home without occupying too much space on the dashboard.

Note that this change does not change the current behaviour. If the config setting is not present, it will list all devices.

Docs PR: home-assistant/home-assistant.io#29255

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New feature (thank you!)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Example configuration

type: energy-devices-graph
max_devices: 3

Additional information

N/A

Checklist

• The code change is tested and works locally.
• There is no commented out code in this PR.
• Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated for www.home-assistant.io

[bramkragten]

This can be merged when documentation for this feature is added.

[frenck]

Added a documentation PR.