Further improved test configuration

Added more tests (#965)

Improved testing ...

After the initializer scripts were removed, we didn't test the actual compose setup anymore. This adds new tests to run the database migrations.

Update postgres Docker tag to v15

Removed unnecessary logging from tests

Initializers are now a plugin

Update dependency redis to v7

Update postgres Docker tag to v14

Use user name instead of userid ...

Nginx unit needs the user and group parameter as names.

Changed entrypoint to "tini".

Update postgres Docker tag to v13

Skip Startup Scripts in Unit Tests

Gunicorn is replaced with nginx-unit ...

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.

Update images in docker-compose

Fixed test failures because of missing cache ...

When running tests with ´test.sh´ some errors where logged because now
redis-cache instance was running.

Improve test.sh ...

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

Building the Docker image with Github Actions