Add --ha-card-border-width

[KTibow]

Proposed change

Add a new variable, --ha-card-border-width for outlined cards.

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

frontend:
  themes:
    test_theme:
      ha-card-border-width: 10px
      ha-card-border-color: purple

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue:
• 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

[KTibow]

Bumping this. I think this could make some things look a bit better:

to

(notice the pixelation)