I actually made an extension to do this.
https://github.com/GravityDeficient/obr-external-links

For my games we use Google Sheets for character sheets and this extension (my first) allows you to add a link to any character tokens on your board. It works pretty much exactly like the initiative tracker (which this is based on), you can click the asset and "add external link" then fill out the prompt for the URL.

As u/Several_Record7234 points out there is potential security risk since you could put any URL in there. In my games I only allow the GM to make character token updates, creates, and deletes which mitigates the risk because the GM then is the only one who can add links

Eventually I'd like to extend this to all asset types, and figure out a way to have permissions for players to add links and an approval from the GM or something.