Default enable header_read_timeout_buffered_io

This enables a HeaderReadTimeout protection for
custom HTTP requests

Changelog: security

config/feature_flags/development/header_read_timeout_buffered_io.yml

@@ -5,4 +5,4 @@ rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/350233
 milestone: '14.8'
 type: development
 group: group::integrations
-default_enabled: false
+default_enabled: true

lib/gitlab/http_connection_adapter.rb

@@ -29,7 +29,7 @@ module Gitlab
       http = super
       http.hostname_override = hostname if hostname
 
-      if Feature.enabled?(:header_read_timeout_buffered_io)
+      if Feature.enabled?(:header_read_timeout_buffered_io, default_enabled: :yaml)
         gitlab_http = Gitlab::NetHttpAdapter.new(http.address, http.port)
 
         http.instance_variables.each do |variable|