Rename DeadMansSwitch to Watchdog

[brancz]

@metalmatze @s-urbaniak @mxinden @squat

[s-urbaniak]

LGTM, but there seems to be some jsonnet update character conversion errors, i.e.:

                              {
-                                  "expr": "max(rate(node_network_transmit_bytes_total{job=\"node-exporter\", instance=\"$instance\", device!~\"lo\"}[5m]))",
+                                  "expr": "max(rate(node_network_transmit_bytes_total{job=\"node-exporter\", instance=\"$instance\", device!\u007e\"lo\"}[5m]))",

[brancz]

Re-generating :)