deployments/metrics: increase prometheus retention

[cirocosta]

this change allows us to keep data collected by prometheus for much longer:

          - name: prometheus-server
            image: "prom/prometheus:v2.13.1"
            imagePullPolicy: "IfNotPresent"
            args:
-             - --storage.tsdb.retention.time=15d
+             - --storage.tsdb.retention.time=60d
              - --config.file=/etc/config/prometheus.yml
              - --storage.tsdb.path=/data
              - --web.console.libraries=/etc/prometheus/console_libraries
              - --web.console.templates=/etc/prometheus/consoles
              - --web.enable-lifecycle

we're currently using ~3.3% of our persistent volume, so it should be quit safe to perform a 4x increase.

Signed-off-by: Ciro S. Costa cscosta@pivotal.io

[cirocosta]

deployed 👍