Add registry validators (#350)

Fixes #96

## Motivation and Context

See #96

## How Has This Been Tested?

Has some unit and integration tests, still needs proper testing of the
different registry types

## Breaking Changes

Yes, new package uploads will need extra verification

## Types of changes
<!-- What types of changes does your code introduce? Put an `x` in all
the boxes that apply: -->
- [ ] Bug fix (non-breaking change which fixes an issue)
- [x] New feature (non-breaking change which adds functionality)
- [x] Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] Documentation update

internal/validators/constants.go

@@ -14,14 +14,13 @@ var (
 	ErrInvalidRemoteURL = errors.New("invalid remote URL")
 
 	// Registry validation errors
-	ErrUnsupportedRegistryType      = errors.New("unsupported registry type")
 	ErrUnsupportedRegistryBaseURL   = errors.New("unsupported registry base URL")
 	ErrMismatchedRegistryTypeAndURL = errors.New("registry type and base URL do not match")
 
 	// Argument validation errors
-	ErrNamedArgumentNameRequired    = errors.New("named argument name is required")
-	ErrInvalidNamedArgumentName     = errors.New("invalid named argument name format")
-	ErrArgumentValueStartsWithName  = errors.New("argument value cannot start with the argument name")
+	ErrNamedArgumentNameRequired     = errors.New("named argument name is required")
+	ErrInvalidNamedArgumentName      = errors.New("invalid named argument name format")
+	ErrArgumentValueStartsWithName   = errors.New("argument value cannot start with the argument name")
 	ErrArgumentDefaultStartsWithName = errors.New("argument default cannot start with the argument name")
 )