Remove grafana api controller and metrics dashboard field

What does this MR do and why?

Remove grafana api controller and update clusters controller.

Remove metrics dashboard url field from GQL type.

Screenshots or screen recordings

NA

How to set up and validate locally

1. Grafana dashboard should return 404 as it does not exist now.
2. metrics_dashboard should not be required in Environments GraphQL API.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #397138 (closed)