Draft: feat(Tokens): integrate design tokens

What does this MR do?

• Add documentation for design tokens
• Remove color variables from _variables.scss
• Import SCSS variables from tokens

Does this MR meet the acceptance criteria?

• The MR title and commit messages meet the Pajamas commit conventions.
• The “What does this MR do?” section in the MR description is filled out, explaining the reasons for and scope of the proposed changes, per “Say why not just what”.
  • For example, if the MR is focused on usage guidelines, addressing accessibility challenges could be added in a separate MR.
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• The MR is added to a milestone.
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• Review requested from any GitLab designer or directly from a maintainer or trainee maintainer.

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