Remove hard coded /etc/pulp/settings.py file

This changes Pulp to not assume any settings file is needed or looked
for at all. It encourages the user to set one via the `PULP_SETTINGS`
Environment Variable. The settings documentation was updated to reflect
this.

The Installer will continue working as is. The PR below causes the
installer to set `PULP_SETTINGS` correctly allowing settings to work
the same way in those environments.

Required PR: pulp/pulp_installer#182

https://pulp.plan.io/issues/5560
closes #5560

CHANGES/5560.feature

@@ -0,0 +1 @@
+Users specify Pulp settings file locaiton and type using `PULP_SETTINGS` environment variable.

docs/installation/configuration.rst

@@ -10,10 +10,20 @@ to configure Pulp in a few ways:
 By Configuration File
 ---------------------
 
-Non-default settings can be specified in the ``/etc/pulp/settings.py``. The presence of this file is
-optional. The expected location and format can be changed by specifying the ``PULP_SETTINGS``
-environment variable. Dynaconf supports `settings in multiple file formats <https://dynaconf.
-readthedocs.io/en/latest/guides/examples.html>`_
+To configure Pulp by settings file, you must set the format and location of the config file by
+specifying the ``PULP_SETTINGS`` environment variable. For example, if you wanted to use Python to
+specify your configuration, and provide it at ``/etc/pulp/settings.py`` you could::
+
+    export PULP_SETTINGS=/etc/pulp/settings.py
+
+
+Or in a systemd file you could::
+
+    Environment="PULP_SETTINGS=/etc/pulp/settings.py" as the Ansible Installer does.
+
+
+Dynaconf supports `settings in multiple file formats <https://dynaconf.readthedocs.io/en/latest/
+guides/examples.html>`_
 
 This file should have permissions of:
 
@@ -32,9 +42,10 @@ If it is in its own directory like ``/etc/pulp``, the directory should have perm
 By Environment Variables
 ------------------------
 
-Each of the settings can also be configured using Dynaconf by prepending ``PULP_`` to the name of
-the setting and specifying that as an environment variable. For example the ``SECRET_KEY`` can be
-specified by exporting the ``PULP_SECRET_KEY`` variable.
+Many users specify their Pulp settings entirely by Environment Variables. Each of the settings can
+be configured using Dynaconf by prepending ``PULP_`` to the name of the setting and specifying that
+as an Environment Variable. For example the ``SECRET_KEY`` can be specified by exporting the
+``PULP_SECRET_KEY`` variable.
 
 
 Settings

pulpcore/app/settings.py

@@ -230,8 +230,6 @@
     INCLUDES_FOR_DYNACONF=[
         '{}.app.settings'.format(plugin_name)
         for plugin_name in INSTALLED_PULP_PLUGINS
-    ] + [
-        "/etc/pulp/settings.py"
     ],
     ENVVAR_FOR_DYNACONF='PULP_SETTINGS',
 )