chore(Favicon): Add storybook favicon

What does this MR do?

Adds a favicon and apple-touch-icon to Storybook to help identify the instance in a browser tab or bookmark. The concept is based on a simple version of the Storybook icon, but replaces the pink with purple, and the S with the tanuki. These are the steps used to add these.

Location	Visual
Chrome before/after
Safari before/after
iOS bookmark

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
  • CustomersDot: mr_url
  • Status Page: mr_url
• [-] Added the ~"component:*" label(s) if applicable.