Add .Values method for enums in bundle config tree (#3278)

## Why
These methods will be used in
#3279 to perform enum validation
for their respective fields.

## Tests
Generated enum_fields.go file has patterns necessary for validating the
fields.

Author: shreyas-goenka

bundle/config/artifact.go

@@ -10,6 +10,13 @@ type ArtifactType string
 
 const ArtifactPythonWheel ArtifactType = `whl`
 
+// Values returns all valid ArtifactType values
+func (ArtifactType) Values() []ArtifactType {
+	return []ArtifactType{
+		ArtifactPythonWheel,
+	}
+}
+
 type ArtifactFile struct {
 	Source string `json:"source"`
 

bundle/config/variable/variable.go

@@ -16,6 +16,13 @@ const (
 	VariableTypeComplex VariableType = "complex"
 )
 
+// Values returns all valid VariableType values
+func (VariableType) Values() []VariableType {
+	return []VariableType{
+		VariableTypeComplex,
+	}
+}
+
 // We alias it here to override the JSON schema associated with a variable value
 // in a target override. This is because we allow for directly specifying the value
 // in addition to the variable.Variable struct format in a target override.

bundle/internal/validation/generated/enum_fields.go

@@ -16,6 +16,15 @@ const (
 	CmdExecutable  ExecutableType = `cmd`
 )
 
+// Values returns all valid ExecutableType values
+func (ExecutableType) Values() []ExecutableType {
+	return []ExecutableType{
+		BashExecutable,
+		ShExecutable,
+		CmdExecutable,
+	}
+}
+
 var finders map[ExecutableType](func() (shell, error)) = map[ExecutableType](func() (shell, error)){
 	BashExecutable: newBashShell,
 	ShExecutable:   newShShell,