Docs: Move dev guide from README (#19707)
Docs: Move dev guide from README (#19707)

* Add docs for overriding default configuration

* Add instructions for building Docker image

* Add docs for end-to-end tests

* Rename to Developer guide

grafana/grafana,grafana/grafana,grafana/grafana,grafana/grafana,grafana/grafana,grafana/grafana,grafana/grafana