Docs: Work on Plugins survey

Twin to https://github.com/grafana/grafana-community-team/issues/672.

Improvements and next steps for the [Plugin Survey](https://docs.google.com/forms/d/1HdIGL1nbVuIOsSyHGjRZEweGqomjtQfA0aAioT9dfoA/edit?ts=691ee952).