allow additional properties in values root

[gertzakis]

Fixes: #287

By allowing additional properties in the root of the schema, anyone can use extra dependencies or pass the same values.yaml file to different helm charts. At the same time, we have safety in nautobot's chart specific scopes.
Meaning:
This is now allowed:

extraKey:
    name: blabla
nautobot:
    image: <nautobot_image>

This will still produce and error and fail:

extraKey:
    name: blabla
nautobot:
    extraKeyNotDefinedInSchema: blabla
ingress:
   extraKeyNotDefinedInSchema: blabla

Because we have "additionalProperties": false under specific objects (eg nautobot, ingress).

[ubajze]

LGTM