[NO-TICKET] Use the external link component in doc site

[pwolfert]

Note that we're going to need to refine the component's styles. I'm putting up this PR early so we have a place to discuss changes we might need to make to that component.

Examples of the problem with using it as-is in blocks of text:

Summary

How to test

Checklist

• [ ] Prefixed the PR title with the Jira ticket number as [WNMGDS-####] Title or [NO-TICKET] if this is unticketed work.
• [ ] Selected appropriate Type (only one) label for this PR, if it is a breaking change, label should only be Type: Breaking
• [ ] Selected appropriate Impacts, multiple can be selected.

If this is a change to code:

• [ ] Created or updated unit tests to cover any new or modified code
• [ ] If necessary, updated unit-test snapshots (yarn test:unit:update) and browser-test snapshots (yarn test:browser:update)

If this is a change to documentation:

• [ ] Checked for spelling and grammatical errors