Allow overriding image registry and Helm chart sources in NetBox deploy script

[pablogarciamiranda]

This PR updates the deploy-netbox.sh script to make it agnostic of any specific image repository or Artifactory instance.

Tests

Without env variables

Deploy netbox into a kind cluster with no ENV variables exported

./deploy-netbox.sh kind "4.1.8" netbox 

Deploy netbox into a vcluster with no ENV variables exported

./deploy-netbox.sh vcluster "4.1.8" netbox --vcluster

With env variables

By exporting the following variables, users can override default URLs and images to point to their repositories:

export NETBOX_HELM_CHART=YOUR_
export POSTGRESS_OPERATOR_HELM_CHART=
export IMAGE_REGISTRY=
export PYPI_REPOSITORY_URL=
export NETBOX_SQL_DUMP_URL=

Deploy netbox into a kind cluster with no ENV variables exported

./deploy-netbox.sh kind "4.1.8" netbox 

Deploy netbox into a vcluster with no ENV variables exported

./deploy-netbox.sh vcluster "4.1.8" netbox --vcluster

[bruelea]

in the netbox-db.yaml the field 'dockerImage' can be added to the spec, to define which image to use for the netbox-db pod. Otherwise it will fail with ImagePullBackOff error.