Add icons for branch and tag in pipeline list

From #17760 (closed):

Talked with @annabeldunstone about this, but recording here for others. One option for handling tags is to include a tag icon to the left of the ref name if it's a tag, and include a branch icon if it's a branch. Then maybe we can drop the [tag] badge.

One problem with this is that we currently using something like the branch icon for forks.

GitHub and Bitbucket use more of a balanced prong thing for forks:

and offshoot prong for branches:

I'm guessing that's because fontawesome only has one symbol, and they call it code-fork. I'd love to see us create custom icons more in line with GitHub and Bitbucket.

/cc @hazelyang