Add dashboard-wide filters

[v-rogg]

It would be really cool to set dashboard-wide filters.

Image you want to filter all insights in one dashboard by appVersion and/or country. Currently, I need to set the filter for each insight separately. While this is only a minor gripe, when the filters don't change over time, but maybe I would like to filter by a newer appVersion. Then I need to update each insight one by one.

Dashboard-wide filters could also make it easier to 'explore' the signals, as I could set up a few insights and quickly swap the filters on them. This could be helpful, for example, if I have multiple insights for 'action' signals. Using dashboard-wide filters, I could now quickly filter and compare different countries/regions or similar.