[CU] Update Icon Storybook docs

[narin]

Description of Change

• Since we will not have an Icon page on our documentation to link to, this updates the autogenerated docs in Storybook for the Icon component
• Adds some additional info on usage, link to assets package, and webpack setup
• Created follow up ticket #234 to update these docs once we've updated our Icons to align with VADS

Testing Packages

N/A

Screenshots/Video

Testing

• [x] Tested on Web

PR Checklist

Code reviewer validation:

• General
  • [x] PR is linked to ticket(s)
  • [x] PR has changelog label applied if it's to be included in the changelog
  • [x] Acceptance criteria:
    • All satisfied or
    • Documented reason for not being performed or
    • Split to separate ticket and ticket is linked by relevant AC(s)
  • [x] Above PR sections adequately filled out
  • [x] If any breaking changes, in accordance with the pre-1.0.0 versioning guidelines: a CU ticket has been created for the VA Mobile App detailing necessary adjustments with the package version that will be published by this ticket
• Code
  • [x] Tests are included if appropriate (or split to separate ticket)
  • [x] New functions have proper TSDoc annotations

Publish

If changes warrant a new version per the versioning guidelines and the PR is approved and ready to merge:

• [x] Merge main into branch
• [x] Merge branch to main
• [ ] Publish new version after merging