build: Move the pylint_django_settings plugin.

When it was located at the root of the project, it was sometimes not
getting loaded correctly since the root of the project is not a python
module, and producing the following error:

```
Command line or configuration file:1:0: E0013: Plugin 'pylint_django_settings' is impossible to load, is it installed ? ('No module named 'pylint_django_settings'') (bad-plugin-value)
```

This led all the pylint tests to fail.

This started happening more as we updated other dependencies via make
upgrade for some reason and led to inconsistent builds.  The move should
hopefully make the loading reliable and consistent.

.editorconfig

@@ -64,7 +64,7 @@
 # SERIOUSLY.
 #
 # ------------------------------
-# Generated by edx-lint version: 5.3.0
+# Generated by edx-lint version: 5.6.0
 # ------------------------------
 [*]
 end_of_line = lf
@@ -97,4 +97,4 @@ max_line_length = 72
 [*.rst]
 max_line_length = 79
 
-# eecef7d3f7f334de2348fe1b4b0b48d605f7dcab
+# 3eb1e01bd9ba6cdf1e5d0a493581c4ea14404b67

openedx/core/tests/pylint_django_settings.py

@@ -1,3 +1,8 @@
+"""
+This is a plugin that helps pylint figure out what DJANGO_SETTINGS_MODULE to use for linting different files.  Since the
+LMS and CMS files have different expectations about what django settings including which installed apps and settings are
+set when the code is run.
+"""
 import os
 import sys
 
@@ -40,7 +45,7 @@ def register(linter):
     """
     Placeholder function to register the plugin with pylint.
     """
-    pass
+    return
 
 
 def load_configuration(linter):

pylintrc

@@ -64,12 +64,12 @@
 # SERIOUSLY.
 #
 # ------------------------------
-# Generated by edx-lint version: 5.4.1
+# Generated by edx-lint version: 5.6.0
 # ------------------------------
 [MASTER]
 ignore = ,.git,.tox,migrations,node_modules,.pycharm_helpers
 persistent = yes
-load-plugins = edx_lint.pylint,pylint_django_settings,pylint_django,pylint_celery,pylint_pytest
+load-plugins = edx_lint.pylint,openedx.core.tests.pylint_django_settings,pylint_django,pylint_celery,pylint_pytest
 
 [MESSAGES CONTROL]
 enable = 
@@ -414,4 +414,4 @@ int-import-graph =
 [EXCEPTIONS]
 overgeneral-exceptions = builtins.Exception
 
-# 5aea7d7fb264005eb373099c856a54cdfa4f311c
+# d6e4348dec0a8eb2752fc4fe02315286c298aeff

pylintrc_tweaks

@@ -1,7 +1,7 @@
 # pylintrc tweaks for use with edx_lint.
 [MASTER]
 ignore+ = ,.git,.tox,migrations,node_modules,.pycharm_helpers
-load-plugins = edx_lint.pylint,pylint_django_settings,pylint_django,pylint_celery,pylint_pytest
+load-plugins = edx_lint.pylint,openedx.core.tests.pylint_django_settings,pylint_django,pylint_celery,pylint_pytest
 
 [MESSAGES CONTROL]
 disable+ =