PMM Server Address: simplify adding address of pmm server

Problem:

1. The flow of connecting to the Percona Platform is complicated in a way - user navigates to Settings and adds data to be connected and then if user forgot to specify the pmm server address, he should navigate to Settings again and fill in all the data. The details of where to go and how to add the pmm-server address also missing in the error message.
2. Adding K8s for DbaaS starts monitoring of K8s cluster, but the feature is not working if Server Address is not set. Currently, we warn users about this and send them to the Settings page. This adds an additional page and step.  But we have a default we can suggest for such cases (URL from the browser)
   

User Story:

• As PMM user (admin) I want to have my PMM server address set automatically when connecting to the Percona Platform.
• As DbaaS admin, I want a faster way to set up server Url   when I'm adding k8s to dbaas, so that I'm not forced to go to a separate page  

Acceptance criteria:

• PMM server address is set automatically when the user connects to Percona Platform.
• PMM server address is set automatically when the user adds K8s to DbaaS. 

UX:

(proposal)

Details:

TBD