Rewrite Server Admin Guide

[gilgongo]

As per https://github.com/jamulussoftware/jamuluswebsite/issues/729 this is a total re-structure, with some light re-writing and minor adjustments here and there.

Points to note BEFORE reading

See my notes here https://github.com/jamulussoftware/jamuluswebsite/issues/729#issuecomment-1328031708

Does this need translation?

YES

Checklist

• [ ] I've verified that this Pull Request follows the general code principles
• [ ] I waited some time after this Pull Request was opened and all GitHub checks completed without errors.
• [x] I'm sure that this Pull Request goes to the correct branch

[gilgongo]

I'm going to re-name this branch as it's a bit confusing. Hope that doesn't screw anything up!

Narrator: It did.