Separate struct validation from JSON package

[darioAnongba]

Currently the json package used to marshal and unmarshal structs is tied to the validator package used to validate entities. Validation and json are unrelated to each other so these packages should be separated

Acceptance criteria

• Remove validation from json package
• Remove global validator using init. Instantiate a validator in components that need one and define their own custom validation functions in the component directly. See manifest reader in infra for an example
• Split yaml and json packages.