Adding GetManifestFiles() and refactoring

[manasachi]

Description

• Added GetManifestFiles function which gets a list of ManifestFiles based on whether given path is a Helm or Kustomize Directory/file, a dir of manifest files, or path to a single manifest file. Note: The existing GetManifestFiles function is renamed to GetManifestFilesFromDir(), so no breaking changes can be introduced in validate.go
• Removes those existing checks from validate.go run().
• Tests will be improved once ManifestFile struct Path property is updated to hold file content as []byte

Fixes # (issue)
Feature # (details)

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Refactor

How Has This Been Tested?

Tested that validate.go does not break with removing code from run(). Added separate test cases for GetManifestFiles()

• Test A
• Test B

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my 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
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[NickKeller]

Looks good - but can you change the import alias to something more descriptive than just h?