feat: added k3s metrics mappings for apps

This change adds mappings to the graphite exporter configuration file that
map the k3s metrics into unified prometheus metrics. When running apps in
TrueNAS scale the pods are exported by the metrics exporter and can be
captured here to get some basic operational details.

The metrics exported are not documented in TrueNAS or k3s in this format, and
this poses a problem making sense of the `cpu` metric.

METRICS.md

@@ -128,4 +128,13 @@ Both memeory statistics from TrueNAS are exported on the onside the physical mem
 |`zfs_prefetch_data_hits_rate`|`op` hit or miss type|`events/s`|Number of hits for the type of cache hit.|
 |`zfs_hash_elements`|`op` current, max|`elements`|Number of hash elements present and maximum.|
 |`zfs_hash_chains`|`op` current, max|`chains`|Number of hash chains present and maximum.|
-|`zfs_pool`|<ul><li>`pool` name of the pool</li><li>`state`</li></ul>|`boolean`|Shows the states of the pool with boolean indicating if they are active.|
+|`zfs_pool`|<ul><li>`pool` name of the pool</li><li>`state`</li></ul>|`boolean`|Shows the states of the pool with boolean indicating if they are active.|
+
+## k3s
+
+|Metric name|Labels|Unit|Description|
+|-----------|------|----|-----------|
+|`k3s_pod_cpu`|`pod` the pod name|`unknown`|A number that represents the cpu usage of the pod. (no documentation)|
+|`k3s_pod_mem`|`pod` the pod name|`bytes`|The number of bytes of memory this pod is using.|
+|`k3s_pod_net`|<ul><li>`pod` the pod name</li><li>`direction` the direction of network traffic</li></ul>|`bytes`|The number of bytes in/out of the pod over the network interface.|
+

graphite_mapping.conf

@@ -488,3 +488,32 @@ mappings:
     job: "truenas"
     instance: "${1}"
     op: "${2}"
+
+################################################
+# k3s mappings
+################################################
+
+- match: 'truenas\.(.*)\.k3s_stats\.k3s_pod_stats\.(.*)\.cpu'
+  match_type: "regex"
+  name: "k3s_pod_cpu"
+  labels:
+    job: "truenas"
+    instance: "${1}"
+    pod: "${2}"
+
+- match: 'truenas\.(.*)\.k3s_stats\.k3s_pod_stats\.(.*)\.mem'
+  match_type: "regex"
+  name: "k3s_pod_mem"
+  labels:
+    job: "truenas"
+    instance: "${1}"
+    pod: "${2}"
+
+- match: 'truenas\.(.*)\.k3s_stats\.k3s_pod_stats\.(.*)\.net\.(.*)'
+  match_type: "regex"
+  name: "k3s_pod_net"
+  labels:
+    job: "truenas"
+    instance: "${1}"
+    pod: "${2}"
+    direction: "${3}"