Add jar as a valid value for artifact type (#3367)

## Why
While settings `type: jar` is non-functional, it is a value we have
documented in our docs. So we should keep it around as a valid value.

## Tests
n/a

Author: shreyas-goenka

bundle/config/artifact.go

@@ -10,10 +10,13 @@ type ArtifactType string
 
 const ArtifactPythonWheel ArtifactType = `whl`
 
+const ArtifactJar ArtifactType = `jar`
+
 // Values returns all valid ArtifactType values
 func (ArtifactType) Values() []ArtifactType {
 	return []ArtifactType{
 		ArtifactPythonWheel,
+		ArtifactJar,
 	}
 }