[Click Behavior] Add a button to return to the source (sign-embedded) dashboard

We have sign-embedded Metabase in Salesforce. We want to use click behavior to show to the users extra info related to some cells (the destination dashboard would be a public dashboard). But they need to be able to go back to the original dashboard (if it was not embedded they could simply click on the back button of the browser to return to where they were).

Suggestion:
Add a back button in the destination dashboard that clicking on it would return the user to the source dashboard.

Implementation Idea:
In click behavior setup, when the behavior is "Go to a custom destination", and the destination is a Metabase link, append the destination link with an extra parameter `&return_url=[url of the current dashboard]` (this needs to be dynamic, meaning if the dashboard is sign-embedded, then the sign-embedded link is used here).
Every time a dashboard loads, parse the url string and if it has the `return_url` parameter, show a button in the dashboard which is a link to the given url.

This is an important feature for us as it allows us to provide valuable info to our sales team in Salesforce.

v.1.43.3

Start by tracing click behavior setup for custom Metabase destinations and the dashboard URL-loading path. Verify how sign-embedded dashboard URLs are represented before deciding how a return URL could be carried between dashboards. Done means a destination dashboard can show a working link back to its source dashboard, including for sign-embedded flows.

Written by the indexing model from the issue text.