finagle: Correct Streaming Metric Name in Doc
finagle: Correct Streaming Metric Name in Doc

Problem
We did not specify the `http` prefix on some streaming metrics in
go/finaglemetrics

Solution
Add the `http` prefix in the metrics description

JIRA Issues: CSL-8508

Differential Revision: https://phabricator.twitter.biz/D342374

twitter/finagle,luciferous/finagle,twitter/finagle,luciferous/finagle,twitter/finagle,luciferous/finagle,luciferous/finagle,twitter/finagle,luciferous/finagle,twitter/finagle,luciferous/finagle