Variables: Save dashboard variables per user

### Discussed in https://github.com/grafana/grafana/discussions/44523 <div type='discussions-op-text'> ^{Originally posted by **yoyo421** January 27, 2022} **What would you like to be added:** Add a fallback if a dashboard variable is not set in the URL query, check what the user set the variable last time **Why is this needed:** If I have a couple of variables, that uses a lot of options, every time I open the dashboard I need to start selecting the variables again from a very long list of options, and it gets really frustrating really fast, because I'm not the owner of the dashboard I cannot save my changes and keep it for the next time (other people working on this dashboard but interested in a different set of selections). Keeping track of the URL every time I change a variable will not help because I open the dashboard from Grafana where the default URL is without the variables.</div>