Add support to gitaly tls

This MR adds the needed configurations to support gitaly tls.

Configurations are added to gitaly in gitaly!932 (merged) and https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/22602

The user will have to have the certificate installed in the system certificate pool by following https://docs.gitlab.com/omnibus/settings/ssl.html#details-on-how-gitlab-and-ssl-work

The user will also need to specify the location of the certificate and the key as gitaly attributes to be able to spin up the server over tls listener

Relates to gitaly#1324 (closed)

Closes #3822 (closed)