Allow redis log location to be user configurable in omnibus package

Allow redis log location to be user configurable.

Add configuration variable redis['log_directory'] to omnibus control via the template file gitlab.rb.template

Requested by EE customer - see 84341

Not able to configure the log location for the redis service, this is available for other services.

To provide consistency for defining logging location for GitLab services.

This would give the ability to move logs out of /var and into a less volatile location.

Gives ability to relocate logs to a different location in a consistent manner.

Customer requested.

Keeps logs in one location.

Make sure these are completed before closing the issue, with a link to the relevant commit.