Add an option to run the polkadot-introspector kvdb exporter as a sidecar

[PierreBesson]

The polkadot-introspector kvdb tool can be used to monitor the database continuously. We should add support for running this exporter as a sidecar in the node helm chart.

We have successfully set it up with this configuration but it feels like a lot of boilerplate to be adding for people who would like to set this up.

extraContainers:
  - name: relaychain-kvdb-introspector
    image: paritytech/polkadot-introspector:438d3406
    command: [
      "polkadot-introspector",
      "kvdb",
      "--db",
      "/data/chains/versi_v1_9/db/full",
      "--db-type",
      "rocksdb",
      "prometheus",
      "--port",
      "9620"
    ]
    resources:
      limits:
        memory: "1Gi"
    ports:
      - containerPort: 9620
        name: relay-kvdb-prom
    volumeMounts:
      - mountPath: /data
        name: chain-data
  - name: parachain-kvdb-introspector
    image: paritytech/polkadot-introspector:438d3406
    command: [
      "polkadot-introspector",
      "kvdb",
      "--db",
      "/data/chains/versi_v1_9/db/full/parachains/db",
      "--db-type",
      "rocksdb",
      "prometheus",
      "--port",
      "9621"
    ]
    resources:
      limits:
        memory: "1Gi"
    ports:
      - containerPort: 9621
        name: para-kvdb-prom
    volumeMounts:
      - mountPath: /data
        name: chain-data

Note there should be the option to run 1 or 2 sidecars. 1 to monitor the main db and 1 for the parachain db (as an option for relay chains).
We also need to create the appropriate ServiceMonitor for loading data in Prometheus.