[Monitoring] Restore dashboard terraform definition (#4561)

This brings back #4497 . The issue was that, in promql definitions, the
'{}' characters were lacking a double escape (\\\\{ and \\\\}).
Also, the only parameter to the terraform object should be
dashboard_json.

Testing: terraform validate


![image](https://github.com/user-attachments/assets/f67434d0-c8e4-4bc0-be38-27188c98ea49)

Part of #4271