Labels change (which occurs e.g. when the metrics resolution is changed on the PMM Settings page) was breaking the MongoDB dashboards

Fix all Formulas in "MongoDB ..." Dashboards

STR

1. Add Mongodb to monitoring
2. Change resolution to Low on PMM Settings
3. Open MongoDB Overview dashboard, MongoDB Instance Summary
   Given result: see screenshot
    

The same problem exists on other Mongo dashboards

Expected result: There is only one line for each instance and there is no any errors on charts