Dashboards: New Grafana panel combining `pt-mysql-summary`, `pt-mongodb-summary`, `pt-pg-summary` outputs

User Story:

As PMM Dashboard developer I need to have a universal single panel for pt-*-summary results, so that I don't need to have a lot of panels to manage

UI: 

the same presentation as we have for pt-summary panel

Instead of implementing  PMM-7159 ,  PMM-7160, PMM-7161 we need to provide a simple panel (can be modified  PMM-3831 ) to present the data.

Acceptance criteria(TBD):

• The panel presents the output of pt-*-summary command for the selected Node or Mysql/Mongo/PG instance selected on the dashboard. Applicable for Single node/Services dashboards only 
• The panel replaces or modifies the panel implemented in PMM-3831  so the PMM doesn't have a lot of similar panels 
• The panel should be configured to show a particular summary type in the panel options
• If the fields required for the panel to work correctly are not part of configured variables, the panel should display an error message

Outcome:

• New Grafana panel for Dashboard. it can be used by people who design dashboards to show pt-*-*summary  data  

How to test:

• Add a panel to a dashboard of your choice
• Select the summary type in the panel options
• Verify that the panel displays the data related to that summary type
• If the fields required for the panel to work correctly are not part of configured variables, verify that the panel displays an error message