Link the sign button to it's original login

[ShrutiK100]

Link the sign in button to its original login page(Jupyter lab login or login specific to the node) until we implement the user login page.

[mishaschwartz]

This is covered in this issue here: DACCS-Climate/Marble-node-registry#36
The website will add a link to the "Sign In" button if the registry contains link with a rel value of "authenticate" for a given node:

https://github.com/DACCS-Climate/marble-website/blob/2c14370b7c34f80dcb93fb2c010de4d178b6c4af/templates/site/js/node.js#L29C14-L29C26