feat(frontend): add repository link components

[JamesDoingStuff]

Adds two components:

• RepositoryLinkBase: has three different variants (icon only, icon + text, disabled) that takes the link address as a prop and renders in the page as a link. Used in the template list & single template pages
• RepositoryLink: relay component built on the above, adding a query that attempts to obtain the templateSource for a given templateRef. Used in the single workflow view.

Also updates many of the existing mock responses to accommodate the new templateSource field