Improvements for better Air-Gapped support

[chrsauer]

During an Airgapped installation, we've faced a serious problem during the deployment of mariadb and redis.

In our environment, without any internet access, we are using JFROG Artifactory with all needed resources.

In this helm chart we would like to entertain the idea to modify the template/deployment.yaml.
The idea is, to do it the same way, as Bitnami is doing it.

For example, in Line 50 an Line 349 (and others) you reference to external containers. The Syntax is:
image: "{{ .Values.image.repository }}:{{ .Values.image.tag }}"

If you modify this into

image: "{{ .Values.image.registry}}/{{ .Values.image.repository }}:{{ .Values.image.tag }}"

and add image.registry to the values.yaml

we will no longer get problems fetching the images from the repo.
The existing format does not work in conjunction with the bitnami files in an air gapped environment.
We always got pull errors, because the reference is to "docker.io" wich can't be reached in an air gapped environment.