Add an option to create an "external link item" in the sidenav

[nikolasburk]

It would be great if in the sidenav, it was possible to add an "external link item" so that we can send people to external resources directly from the docs.

More context in this internal thread:

[meletj]

See the experiment from Alex here: #4817 with the examples projects.
The ask would then be for the playground (as it is an external link).

[nilubava]

Blocked: Look into other options (maybe in Quickstart?) @meletj

[jharrell]

@nikolasburk still required?

[nikolasburk]

Def would be nice to have but in our efforts to clean up issues, I'll close this one for now.