Imaginator: add flag to by default inherit computed files, filters and triggers.

[narendraReddy45]

Description & Motivation

This PR introduces -enableDefaultInheritance flag to imaginator and builder-tool. When this flag is enabled, child images inherit triggers, filters and computed-files from sourceImage without need of empty .add files

This also maintains backward compatibility for existing image manifests functionality

Behavior matrix

Note: "metadata file" below refers to filter , computed-files or triggers

Child Manifest Directory state	Without Flag ( Default / Backward Compatible )	With -enableDefaultInheritance Flag
Neither file nor .add file is present	Empty Child has no metadata.	Inherits Child inherits metadata exactly as defined in base image.
File exists but is empty and valid	Empty Child has no metadata.	Empty Child has no metadata.
File exists with content	Replaces Child uses its own metadata.	Replaces Child uses its own metadata.
.add file exists	Merges Child appends rules to base metadata	Merges Child appends rules to base metadata

Fixes #247

Type of Change

• New feature (non-breaking change which adds functionality)
• Documentation update

How Has This Been Tested?

• Build images with tests cases as described in above behavior matrix

Testing Approach

Build images using local imageserver, imaginator, builder-tool and verify files based on test cases for desired results

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works