Add headers to indicate remote read/write version
Add headers to indicate remote read/write version

Also add Content-Type header.

amorken/prometheus,Gouthamve/prometheus,Conorbro/prometheus,tomwilkie/prometheus,brancz/prometheus,brancz/prometheus,kzittritsch/prometheus,brancz/prometheus,Stackdriver/stackdriver-prometheus,tomwilkie/prometheus,keegancsmith/prometheus,kzittritsch/prometheus,amorken/prometheus,AlekSi/prometheus,alileza/prometheus,keegancsmith/prometheus,SaltedMan/prometheus-annotated,AlekSi/prometheus,GoogleCloudPlatform/prometheus,Gouthamve/prometheus,Colstuwjx/prometheus,JavierZunzunegui/prometheus,Conorbro/prometheus,Gouthamve/prometheus,GoogleCloudPlatform/prometheus,yanghongkjxy/prometheus,Stackdriver/stackdriver-prometheus,alileza/prometheus,Conorbro/prometheus,alileza/prometheus,dsymonds/prometheus,Conorbro/prometheus,alileza/prometheus,Gouthamve/prometheus,Colstuwjx/prometheus,SaltedMan/prometheus-annotated,kzittritsch/prometheus,GoogleCloudPlatform/prometheus,keegancsmith/prometheus,dsymonds/prometheus,Stackdriver/stackdriver-prometheus,GoogleCloudPlatform/prometheus,JavierZunzunegui/prometheus,tomwilkie/prometheus,prometheus/prometheus,dsymonds/prometheus,prometheus/prometheus,prometheus/prometheus,amorken/prometheus,SaltedMan/prometheus-annotated,tomwilkie/prometheus,keegancsmith/prometheus,kangwoo/prometheus,Colstuwjx/prometheus,alileza/prometheus,yanghongkjxy/prometheus,brancz/prometheus,AlekSi/prometheus,AlekSi/prometheus,kangwoo/prometheus,SaltedMan/prometheus-annotated,prometheus/prometheus,yanghongkjxy/prometheus,keegancsmith/prometheus,JavierZunzunegui/prometheus,kangwoo/prometheus,dsymonds/prometheus,yanghongkjxy/prometheus,kangwoo/prometheus,Stackdriver/stackdriver-prometheus,amorken/prometheus,kzittritsch/prometheus,prometheus/prometheus,JavierZunzunegui/prometheus,Colstuwjx/prometheus,GoogleCloudPlatform/prometheus