Allow specifying port through PAPERLESS_PORT environment variable

docs/configuration.rst

@@ -699,6 +699,12 @@ PAPERLESS_WEBSERVER_WORKERS=<num>
 
     Defaults to 2.
 
+PAPERLESS_PORT=<port>
+    The port number the webserver will listen on. Change the port if it collides
+    with other services in your setup.
+
+    Defaults to 8000.
+
 USERMAP_UID=<uid>
     The ID of the paperless user in the container. Set this to your actual user ID on the
     host system, which you can get by executing

gunicorn.conf.py

@@ -1,6 +1,6 @@
 import os
 
-bind = '0.0.0.0:8000'
+bind = f'0.0.0.0:{os.getenv("PAPERLESS_PORT", 8000)}'
 workers = int(os.getenv("PAPERLESS_WEBSERVER_WORKERS", 2))
 worker_class = 'paperless.workers.ConfigurableWorker'
 timeout = 120