Update systemd service template

[martinnj]

Pull Request

What does this PR do?

• It adds automatic restart to the systemd service template in the "Running in Production" section

The motivation is that if the service crashes (like from 6/ABRT errors during memory allocation, something I've seen several times during the last week) it should restart automatically and not stay dead until manual intervention.

Feedback wanted

• I set it to Restart=always because that is what I needed for my usage, but I know some maintainers prefer the more conservative on-failure or on-abort behavior. I can substitute that if you'd rather have that.
• The fix for the too_many_open_files error described in the docs here also requires a fix in this file, basically you have to set LimitNOFILE=<howevermanyfilesyouwant> should I add that in this PR as well?