Add manual limit selection to graph header/footer

[thomasloven]

Proposed change

Add a manual y-limit selection to graph header/footer and sensor cards.

type: sensor
entity: sensor.temperature2
graph: line
detail: 2
hours_to_show: 1
limits:
  min: 0
  max: 30
name: 'Manual limits [0,30]'

Default limits still automatically fit the data unless any unit_of_measurement is %. Then the default are 0-100.

No GUI editor.

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

Additional information

Edit 2021-07-18:

A bit of background and discussion can be found on discord, starting here and continuing a few dozen messages: https://discord.com/channels/330944238910963714/351047592588869643/837837258743873577

• This PR fixes or closes issue: fixes #
• This PR is related to issue or discussion:
• Link to documentation pull request:

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

[balloob]

🎉