Add alert status for extended and simple output

[ffahri]

Closes #2204
Signed-off-by: Fahri Yardımcı

Added state field into both simple and extended output.

sometimes extended output can be a bit long and can be hard to read sometimes therefore finding the alert state in simple output can things much easier.

Extended output

$ ./amtool --alertmanager.url http://alertmanager:9093 alert query -o extended -s -a  'alertname="Watchdog"'
Labels                                                            Annotations  Starts At  Ends At  Generator URL  State
alertname="Watchdog" prometheus="test" severity="none"  message="This is an alert meant to ensure that the entire alerting pipeline is functional.
"                                                                 2020-07-10 11:00:00 UTC  2020-07-16 16:00:00 UTC  http://prom:9090/graph?g0.expr=vector%281%29&g0.tab=1  active

Simple output

$ ./amtool --alertmanager.url http://alertmanager:9093 alert query  -s -a  'alertname="Watchdog"'
Alertname  Starts At                Summary  State
Watchdog   2020-07-10 11:00:00 UTC           active

Not sure about the state field order in extended output ?

[simonpasquier]

Thanks! I think it makes sense to have the alert's state in the simple output and if we have it there, it should in the extended output too.