The Gunicorn server should be configurable with regard to the address, the port and the user.

**Background**
The Gunicorn server should be configurable with regard to the address, the port and the user. This increases flexibility when used in Kubernetes or a multi-service environment.

**Solution**
Adjustment of the gunicorn.auto.conf -> https://github.com/epam/Indigo/blob/1b5bb8808b73b6613d2e96b9a95eefc6b1a15b02/utils/indigo-service/backend/conf/gunicorn.auto.conf
And Default Envs in the Dockerfile -> https://github.com/epam/Indigo/blob/1b5bb8808b73b6613d2e96b9a95eefc6b1a15b02/utils/indigo-service/backend/Dockerfile

gunicorn.auto.conf:

```
[program:gunicorn]
directory=/srv/api
user=%(ENV_guuser)s

command=/bin/bash -c "gunicorn --bind %(ENV_guaddress)s:%(ENV_guport)s --workers=$(nproc) app:app"
autostart=true
autorestart=true

redirect_stderr=true
stdout_logfile=/dev/stdout
stdout_logfile_maxbytes=0
killasgroup=true
```

dockerfile (add):
```
# default gunicorn bind
ENV guaddress 0.0.0.0
ENV guport 80
# default gunicorn user
ENV guuser root

```
**Alternatives**
--

**Additional context**
--

Start with utils/indigo-service/backend/conf/gunicorn.auto.conf and utils/indigo-service/backend/Dockerfile. Check how the Gunicorn command and environment defaults are currently defined, then verify that address, port, and user can be configured while the supplied defaults still allow the service to start correctly.

Written by the indexing model from the issue text.