Add Fingerprint ID in data

[marcusteixeira]

Add a Fingerprint support data in event logs.

• https://github.com/prometheus/alertmanager/issues/1903

[marcusteixeira]

In this example, show the fingerprint data in search of elasticsearch.

only main_test.go which does not seem to work but is still detecting the problem.

[marcusteixeira]

@ageis, @mattbostock, @simonpasquier