update .gitignore to keep extra.py in ldap config

Lint the syntax of changes

Ignore prometheus.yml

Rename example.py to extra.py ...

And add some comments to the the file that hopefully guide the user.

Ignore non-default configuration files

Remove the 'X-Forwarded-Proto' line from the nginx config ...

The reason is that in the default configuration nginx is only serving 'http' traffic.
So if an upstream proxy sets the 'X-Forwarded-Proto' header, because it is terminating
TLS, then nginx will overwrite it to 'http'. This will cause django to think the page
is served via 'http' and it will not create 'https://...' URLs.

Related to #292

Improve test.sh ...

Don't move the original initializers directory, but rather use the one
with the modified initializers in it.

Ignore local override file ...

Adding an ignore rule for docker-compose.override.yml should allow people to clone this repo and use an override file to match their environment, without that file causing issues every time they pull a new version of the repo.

externalize netbox download with wget

❇️ Make the default configuration cluster ready ...

This changes the default configuration to be better prepared for
usage with container management platforms, such as Docker Swarm,
Kubernetes or OpenShift.

Closes #27.