Draft: Add success and warning input validation options

What does this MR do?

Adds success and warning validation options to gl-form-group to compliment the existing error state.

• See gitlab-org/gitlab-services/design.gitlab.com#706 (closed) where this was added to the design specs.
• See gitlab-org/gitlab-services/design.gitlab.com!2095 (merged) for documentation changes to Pajamas.

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines.
• GitLab UI's contributing guidlines.
• If it changes a Pajamas-compliant component's look & feel, the MR has been reviewed by a UX designer.
• If it changes GitLab UI's documentation guidelines, the MR has been reviewed by a Technical Writer.
• If the MR changes a component's API, integration MR(s) have been opened in the following projects to ensure that the @gitlab/ui package can be upgraded quickly after the changes are released:
  • GitLab: mr_url
  • Customers Portal: mr_url
  • Status Page: mr_url
• Added the ~"component:*" label(s) if applicable.

Closes #1073 (closed)