feat: validate groups and kinds, fix double processing

[scottd018]

This PR improves a few items of interest:

• Fixes #270 - Validates that component kinds are unique within the groups
• Fixes #262 - Removes double parsing of entire resource manifests
• Refactors files into their own independent packages

[lander2k2]

Naming suggestions for the internal/workload/v1/resources package...

internal/workload/v1/
...
└── child_resources
    ├── child_resources.go
    ├── input_manifest.go
    └── output_source_file.go

Adding input_ and output_ helps conceptualized the flow of data. And child_ helps clarify the vagueness of resources.