New Resource - All Appearance API fields

New Data Source / Resource

Would be nice to configure all fields of Appearance API.
But in my case I'm interested in description, since sign_in_text and help_text of Settings API got deprecated: https://docs.gitlab.com/ee/update/deprecations.html#deprecated-parameters-related-to-custom-text-in-the-sign-in-page

Related GitLab APIs

API documentation:

• https://docs.gitlab.com/ee/api/appearance.html

Additional Details

• GitLab REST API resources available (read for data sources, crud for resources)
• go-gitlab does support the related GitLab API already
• I'd like to contribute it myself