Use dashboard parameters in textbox widgets

[tndhagedorn]

It would be very helpful if I could reference a dashboard's query parameters in any textbox widgets on that dashboard, using the same templating (mustache?) as can be done with chart labels or table links

This is similar to the feature request for dashboard titles #4383.

I often find non-technical dashboard users may need more context for the content on the dashboard, and being able to generate text using dashboard parameters would really help with this.