Configurable container images for cert-csi

[rishabhatdell]

Description

This PR allows cert-csi to use custom images for creating containers by passing an image config YAML file as an argument. The YAML file should have linux(test) and postgres images name with their corresponding image URL. For example:

images:
  - test: "docker.io/centos:centos7"
    postgres: "docker.io/bitnami/postgresql:11.8.0-debian-10-r72"

To use this feature, run cert-csi with the option --image-config /path/to/config.yaml along with any other arguments.

GitHub Issues

List the GitHub issues impacted by this PR:

GitHub Issue #
https://github.com/dell/csm/issues/1059

Checklist:

• I have performed a self-review of my own code to ensure there are no formatting, vetting, linting, or security issues
• I have verified that new and existing unit tests pass locally with my changes
• I have not allowed coverage numbers to degenerate
• I have maintained at least 90% code coverage
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I have maintained backward compatibility

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Please also list any relevant details for your test configuration

• Built binary and executed unit tests
  

• Executed the cert-csi to verify whether the provided image was utilized in the container build process
  

[atye]

Will there be a csm-docs update describing how to use this?

[adarsh-dell]

Can we enhance this log by stating that 'docker.io/centos:latest' is the default image?

[adarsh-dell]

@rishabhatdell , what are your thoughts on incorporating a generic/common function to eliminate code duplication? It seems we've duplicated the same logic across multiple sections, checking for the same conditions in each suite.

[rishabhatdell]

Will there be a csm-docs update describing how to use this?

here is the PR: dell/csm-docs#928

[gallacher]

LGTM

[AkshaySainiDell]

LGTM