feat(GlTokenSelector): Implement token selector component

What does this MR do?

Adds a "Token Selector" component.

• See #798 (closed) for spec
• See gitlab#33143 (comment 333784563) for initial discussion about design/functionality

Examples

Basic

User Defined Tokens

User Tokens

Review App

http://add-token-selector-component.162.243.131.170.nip.io/?path=/story/base-token-selector--default

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.