Make workhorse.trustedCIDRsForXForwardedFor default to trusted_proxies

Summary

We just merged a fix for Workhorse (gitlab-org/gitlab!189530 (merged)) not being able to extract the real remote_ip when multiple proxies are in the loop: gitlab-org/gitlab#325078 (closed). This requires specifying the trusted_cidrs_for_x_forwarded_for setting in Workhorse's config.toml, which is similar to the trusted_proxies config.

Currently the webservice has the trusted_proxies setting. We should probably default trusted_cidrs_for_x_forwarded_for to that value if it is specified.