Allow access using Basic Authentication prefix

Enable the use of '/a/' prefix to the monitoring URL to allow external
authenticated access to the monitoring data (e.g. Prometheus
integration):

  GET /a/monitoring?format=prometheus

Test Plan:

  curl --basic -u user:secret \
     http://gerrit.mycompany.com/a/monitoring?format=prometheus

Bug: Issue 9550
Inspired-By: evernat <evernat@free.fr>
Change-Id: Iecfe4fd2ea79fb19c02a81b181e78df01f73cd1b
1 file changed