konga node data and user data (via configmaps and mounts)

[andrevtg]

This PR allows using KONGA_SEED_KONG_NODE_DATA_SOURCE_FILE and KONGA_SEED_USER_DATA_SOURCE_FILE with the Helm Chart to seed an admin user and a kong admin endpoint by mounting such files with a configmap.

The configmap should provide content for konga_node.data and konga_user.data like in the example below (please notice that kong_admin_url is an "in-cluster" url):

data:
  konga_node.data: |-
    module.exports = [
        {
            "name": "kong-admin",
            "type": "key_auth",
            "kong_admin_url": "http://your-kong-admin:8444",
            "health_checks": false,
        }
    ]

  konga_user.data: |-
    module.exports = [
        {
            "username": "admin",
            "email": "admin@somewhere.com",
            "admin": true,
            "active" : true,
            "password": "somepassword"
        }
    ]