Set SSL_CERT_DIR=/opt/gitlab/embedded/ssl/certs/ for gitlab-pages

Omnibus needs to set SSL_CERT_DIR=/opt/gitlab/embedded/ssl/certs/ for the gitlab-pages service.

#3701 (comment 111629540) noted:

the Pages service template was created in such a way that it explicitly set SSL_CERT_FILE in the exec entry of the generated run command for runit.

In gitlab-pages!291 (merged) I noted that omnibus-gitlab will need to set SSL_CERT_DIR.

This is part of gitlab#25411 (closed).

I currently have to hack around this with the following change to /opt/gitlab/sv/gitlab-pages/run:

- exec /usr/bin/env SSL_CERT_FILE=/opt/gitlab/embedded/ssl/certs/cacert.pem \
+ exec /usr/bin/env SSL_CERT_FILE=/opt/gitlab/embedded/ssl/certs/cacert.pem SSL_CERT_DIR=/opt/gitlab/embedded/ssl/certs/ \

cc @jacobvosmaer-gitlab @WarheadsSE @vshushlin @jmeshell