Initial dedicated docs for Flask config options.

Flask-RESTX makes use of a number of Flask configuration options. These
are either undocumented or scattered throughout the documentation. This
commit introduces an initial list of all options in a dedicated
documentation page. The previously undocumented RESTX_JSON contains
additional detail in response to an issue apryor6/flask_accepts#69 (comment)

Signed-off-by: Ben Steadman <steadmanben1@gmail.com>

Author: SteadBytes

doc/configuration.rst

@@ -0,0 +1,42 @@
+Configuration
+=============
+
+Flask-RESTX provides the following `Flask configuration values <https://flask.palletsprojects.com/en/1.1.x/config/#configuration-handling>`_:
+
+    Note: Values with no additional description should be covered in more detail
+    elsewhere in the documentation. If not, please open an issue on GitHub.
+
+.. py:data:: RESTX_JSON
+
+    Provide global configuration options for JSON serialisation as a :class:`dict`
+    of :func:`json.dumps` keyword arguments.
+
+.. py:data:: RESTX_VALIDATE
+
+.. py:data:: RESTX_MASK_HEADER
+
+.. py:data:: RESTX_MASK_SWAGGER
+
+.. py:data:: RESTX_INCLUDE_ALL_MODELS
+
+.. py:data:: BUNDLE_ERRORS
+
+.. py:data:: ERROR_404_HELP
+
+.. py:data:: HTTP_BASIC_AUTH_REALM
+
+.. py:data:: SWAGGER_VALIDATOR_URL
+
+.. py:data:: SWAGGER_UI_DOC_EXPANSION
+
+.. py:data:: SWAGGER_UI_OPERATION_ID
+
+.. py:data:: SWAGGER_UI_REQUEST_DURATION
+
+.. py:data:: SWAGGER_UI_OAUTH_APP_NAME
+
+.. py:data:: SWAGGER_UI_OAUTH_CLIENT_ID
+
+.. py:data:: SWAGGER_UI_OAUTH_REALM
+
+.. py:data:: SWAGGER_SUPPORTED_SUBMIT_METHODS

doc/index.rst

@@ -55,6 +55,7 @@ Flask-RESTX with Flask.
     postman
     scaling
     example
+    configuration
 
 
 API Reference