Storybook > Backport the LinkToSource block from GitLab UI

In GitLab UI's Storybook, we have implemented a LinkToSource docs block to add a link to the component's source in its docs page.

We could benefit from the same functionality in GitLab's Storybook.

We could choose to replicate the same implementation in the GitLab project. Another option might be to bundle GitLab UI's docs blocks in a NPM package that would make it easier to share features across our Storybooks.