Allowing ability to use your own Custom image while Using DeploymentScript resource

**Is your feature request related to a problem? Please describe.**
We were planning to deploy some apps which required the presence of some libraries, so ran in to issues while doing that as there was no clear path to deploy some of the libraries.

**Describe the solution you'd like**
Ability to extend from the base image to add depenencies and use custom images for DeploymentScripts

Start by reading the current DeploymentScript resource behavior and how its base image and dependencies are defined. Determine the supported scope for extending the base image or supplying a custom image; done means a documented and validated path for deploying required libraries with DeploymentScript.

Written by the indexing model from the issue text.