Add POST handler for /debug to fix CPU profiling.
Add POST handler for /debug to fix CPU profiling.

`go tool pprof` sends a POST request to enable CPU profiling, so we also
need to handle that method.

PrFalken/prometheus,dln/prometheus,prometheus/prometheus,kzittritsch/prometheus,dpatel06/prometheus,Dieterbe/prometheus,AlekSi/prometheus,dmilstein/prometheus,datajet-io/prometheus,tomwilkie/prometheus,sudhi-vm/prometheus,agaoglu/prometheus,sudhi-vm/prometheus,SaltedMan/prometheus-annotated,tattsun/prometheus,brancz/prometheus,dmilstein/prometheus,gcnonato/prometheus,gcnonato/prometheus,dmilstein/prometheus,Gouthamve/prometheus,PrFalken/prometheus,dpatel06/prometheus,keegancsmith/prometheus,wrouesnel/prometheus,iksaif/prometheus,msiebuhr/prometheus,alileza/prometheus,alileza/prometheus,Gouthamve/prometheus,dsymonds/prometheus,jimmidyson/prometheus,Conorbro/prometheus,slok/prometheus,flier/prometheus,dln/prometheus,JavierZunzunegui/prometheus,AlekSi/prometheus,Dieterbe/prometheus,dln/prometheus,mtanda/prometheus,ton31337/prometheus,wrouesnel/prometheus,GoogleCloudPlatform/prometheus,tattsun/prometheus,wxdublin/prometheus,datajet-io/prometheus,brancz/prometheus,iksaif/prometheus,ton31337/prometheus,SaltedMan/prometheus-annotated,PrFalken/prometheus,gcnonato/prometheus,prometheus/prometheus,gcnonato/prometheus,gottwald/prometheus,GoogleCloudPlatform/prometheus,sudhi-vm/prometheus,AlekSi/prometheus,jbdalido/prometheus,keegancsmith/prometheus,PrFalken/prometheus,dsymonds/prometheus,ton31337/prometheus,GoogleCloudPlatform/prometheus,wrouesnel/prometheus,JavierZunzunegui/prometheus,kangwoo/prometheus,Stackdriver/stackdriver-prometheus,Colstuwjx/prometheus,iksaif/prometheus,slok/prometheus,Gouthamve/prometheus,SaltedMan/prometheus-annotated,yanghongkjxy/prometheus,dsymonds/prometheus,kzittritsch/prometheus,prometheus/prometheus,SaltedMan/prometheus-annotated,yanghongkjxy/prometheus,jbdalido/prometheus,adamron1/prometheus,Conorbro/prometheus,RobertKielty/prometheus,GoogleCloudPlatform/prometheus,kangwoo/prometheus,Conorbro/prometheus,kzittritsch/prometheus,amorken/prometheus,Colstuwjx/prometheus,agaoglu/prometheus,Gouthamve/prometheus,jbdalido/prometheus,thachmai/prometheus,flier/prometheus,nicr9/prometheus,yanghongkjxy/prometheus,eliothedeman/prometheus,amorken/prometheus,adamron1/prometheus,tomwilkie/prometheus,JavierZunzunegui/prometheus,adamron1/prometheus,eliothedeman/prometheus,ton31337/prometheus,agaoglu/prometheus,slok/prometheus,gottwald/prometheus,msiebuhr/prometheus,nicr9/prometheus,jbdalido/prometheus,yanghongkjxy/prometheus,RobertKielty/prometheus,keegancsmith/prometheus,eliothedeman/prometheus,Conorbro/prometheus,trigrass2/prometheus,prometheus/prometheus,dpatel06/prometheus,RobertKielty/prometheus,dsymonds/prometheus,alileza/prometheus,trigrass2/prometheus,eliothedeman/prometheus,trigrass2/prometheus,jimmidyson/prometheus,jimmidyson/prometheus,mtanda/prometheus,kzittritsch/prometheus,dalanlan/prometheus,alileza/prometheus,JavierZunzunegui/prometheus,keegancsmith/prometheus,GoogleCloudPlatform/prometheus,thachmai/prometheus,datajet-io/prometheus,Colstuwjx/prometheus,kangwoo/prometheus,wrouesnel/prometheus,dalanlan/prometheus,trigrass2/prometheus,slok/prometheus,thachmai/prometheus,RobertKielty/prometheus,wxdublin/prometheus,mtanda/prometheus,wxdublin/prometheus,keegancsmith/prometheus,kangwoo/prometheus,gottwald/prometheus,prometheus/prometheus,alileza/prometheus,iksaif/prometheus,Dieterbe/prometheus,tattsun/prometheus,tattsun/prometheus,dmilstein/prometheus,msiebuhr/prometheus,sudhi-vm/prometheus,Stackdriver/stackdriver-prometheus,nicr9/prometheus,brancz/prometheus,agaoglu/prometheus,dln/prometheus,thachmai/prometheus,dalanlan/prometheus,Colstuwjx/prometheus,Stackdriver/stackdriver-prometheus,Stackdriver/stackdriver-prometheus,flier/prometheus,adamron1/prometheus,msiebuhr/prometheus,tomwilkie/prometheus,AlekSi/prometheus,gottwald/prometheus,amorken/prometheus,mtanda/prometheus,amorken/prometheus,datajet-io/prometheus,tomwilkie/prometheus,brancz/prometheus