* modules/rosenthal/services/monitoring.scm (prometheus-activation): Fix
permission for /var/lib/prometheus, which is also used by
prometheus-node-exporter.
* modules/rosenthal/services/monitoring.scm (<prometheus-configuration>): New
data type.
(prometheus-account, prometheus-activation, prometheus-shepherd): New
procedures.
(prometheus-service-type): New variable.
* modules/rosenthal/services/monitoring.scm (<grafana-configuration>): New data
type.
(grafana-account, grafana-postgresql-role, grafana-activation)
(grafana-shepherd): New procedures.
(grafana-service-type): New variable.
