Fixes failing startup because of python error:
```
Traceback (most recent call last):
File "/opt/netbox/netbox/./manage.py", line 10, in <module>
execute_from_command_line(sys.argv)
File "/opt/netbox/venv/lib/python3.10/site-packages/django/core/management/__init__.py", line 446, in execute_from_command_line
utility.execute()
File "/opt/netbox/venv/lib/python3.10/site-packages/django/core/management/__init__.py", line 440, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File "/opt/netbox/venv/lib/python3.10/site-packages/django/core/management/base.py", line 402, in run_from_argv
self.execute(*args, **cmd_options)
File "/opt/netbox/venv/lib/python3.10/site-packages/django/core/management/base.py", line 448, in execute
output = self.handle(*args, **options)
File "/opt/netbox/venv/lib/python3.10/site-packages/django/core/management/commands/shell.py", line 127, in handle
exec(sys.stdin.read(), globals())
File "<string>", line 2, in <module>
File "/opt/netbox/venv/lib/python3.10/site-packages/django/db/models/manager.py", line 85, in manager_method
return getattr(self.get_queryset(), name)(*args, **kwargs)
File "/opt/netbox/venv/lib/python3.10/site-packages/django/db/models/query.py", line 650, in get
raise self.model.DoesNotExist(
users.models.Token.DoesNotExist: Token matching query does not exist.
```
When the container is started as root the default was to drop privileges to "unit:unit". This caused some problems with temporary files. Now the privileges are drop to "101:0".
When the container is started as a normal user unit prints a warning that changing the user and group is not possible. This warning is safe to ignore.
The migrations are only started if there are some that have not been
applied. Additionally the maintenace task needed after an update are
now run after the migrations
Before, the main_config (e.g. 'configuration.py' or 'ldap_config.py') were loaded twice.
The first load was hard-coded and correct.
The second load was during the discovery phase for dynamic configurations.
This has now been fixed. During the discovery for dynamic configurations,
the main_config file is now excluded.
Thanks @tobiasge for discovering this bug.
We now serve Netbox with an nginx-unit instance instead of Gunicorn.
This allows us to get rid of the extra Nginx container because Unit is
also serving the static files. The static files are now collected at container
buildtime instead of every startup.
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
