Currently, the only mechanism for extending the model generation is to use a BuildMutateHook at the end of the model generation process. This can be quite limiting as the hook only has scope of the model build and not the graphql schema which has been parsed.

This change adds a hook at the end of the field creation process which provides access to the parsed graphql type definition and field definition. This allows for more flexibility for example adding additional tags to the model based off custom directives

# Conflicts:
#	plugin/modelgen/models.go