[US] Configure buildpacks image configuration through JKube's image configuration

[rohanKanojia]

Component

JKube Kit

Task description

Part of #439

Related to #2457

As a user, I want to be able to provide a ImageConfiguration for the buildpack strategy, so that I can customize the generated container image.
These are the option to cover:

• ImagePullPolicy
• Tags
• Environment variables
• Volumes

Expected Behavior

As a user, If I specify imagePullPolicy, tags, environment variable via standard image configuration. I should be able to see them reflected in image created via Buildpacks

Acceptance Criteria

Given:

• User is using buildpacks build strategy
• User configures some aspect of image via XML/Groovy DSL configuration

When:

• User performs k8s:build/k8sBuild

Then:

• Aspects of image configured via image configuration (tags, environment variables) should be present in the final image generated by JKube using buildpacks build strategy.