Add Prometheus metrics relabel configuration for exporters

Tested succesfully with the following test cases:
            source_labels: instance
            source_labels: instance,__name__,test
            source_labels: [instance,__name__,test]
            source_labels:
              - instance
              - __name__
              - test

Change-Id: I9750bb0a4204335dd202cc4020445e850824c497
Depends-On: I2f85fe2f9cc67d2d03d5e8dad5ac0b74e82b0fcc
1 file changed