Add routing validation
Add routing validation

The root route in the configuration must not exclude any alerts,
i.e. not have any matchers.
All receivers referenced in the routing tree are validated to exist.

sarathsp06/alertmanager,brancz/alertmanager,GoogleCloudPlatform/alertmanager,GoogleCloudPlatform/alertmanager,brunoqc/alertmanager,prometheus/alertmanager,ericgerling/alertmanager,tyrken/alertmanager,ericgerling/alertmanager,novilabs/alertmanager,joehandzik/alertmanager,tyrken/alertmanager,brancz/alertmanager,joehandzik/alertmanager,novilabs/alertmanager,prometheus/alertmanager,Aloomaio/alertmanager,tinytub/alertmanager,Kellel/alertmanager,Aloomaio/alertmanager,tyrken/alertmanager,prometheus/alertmanager,Aloomaio/alertmanager,brunoqc/alertmanager,Kellel/alertmanager,tinytub/alertmanager,prometheus/alertmanager,tinytub/alertmanager,Kellel/alertmanager,brunoqc/alertmanager,tyrken/alertmanager,tbouvet/alertmanager,novilabs/alertmanager,GoogleCloudPlatform/alertmanager,tbouvet/alertmanager,brancz/alertmanager,joehandzik/alertmanager,brunoqc/alertmanager,ericgerling/alertmanager,sarathsp06/alertmanager,tbouvet/alertmanager,novilabs/alertmanager,sarathsp06/alertmanager,GoogleCloudPlatform/alertmanager,brancz/alertmanager