Add a OpenAPIProvider to allow for customisation

By overridding and changing the OpenAPIProvider the generated OpenAPI
can be customised as desired. This should, I hope, fulfill a number of
feature requests for various customisation aspects.

docs/how_to_guides/customising.rst

@@ -0,0 +1,57 @@
+Customising the OpenAPI schema
+==============================
+
+The generation of the OpenAPI schema by Quart-Schema can be customised
+by changing the :attr:`QuartSchema.openapi_provider_class`. For
+example to only include routes within a specific blueprint named
+``bp``,
+
+.. code-block:: python
+
+    from quart_schema import OpenAPIProvider, QuartSchema
+
+    class BlueprintOnlyOpenAPIProvider(OpenAPIProvider):
+        def __init__(self, blueprint_name: str, app: Quart, extension: QuartSchema) -> None:
+            super().__init__(app, extension)
+            self._blueprint_prefix = f"{blueprint_name}."
+
+        def generate_rules(self) -> Iterable[Rule]:
+            for rule in self._app.url_map.iter_rules():
+                hidden = getattr(
+                    self._app.view_functions[rule.endpoint], QUART_SCHEMA_HIDDEN_ATTRIBUTE, False
+                )
+                if rule.endpoint.beginswith(self._blueprint_prefix) and not hidden and not rule.websocket:
+                    yield rule
+
+    quart_schema = QuartSchema(app, openapi_provider_class=CustomerOpenAPIProvider)
+
+
+It is also possible to alter how the operation ID is generated,
+
+.. code-block:: python
+
+    from quart_schema import OpenAPIProvider, QuartSchema
+
+    class CustomOperationIdOpenAPIProvider(OpenAPIProvider):
+        def operation_id(self, method: str, func: Callable) -> Optional[str]:
+            return func.__name__
+
+    quart_schema = QuartSchema(app, openapi_provider_class=CustomerOpenAPIProvider)
+
+There are many more aspects that can be customised, see the
+:class:`OpenAPIProvider` for options.
+
+Custom routes
+-------------
+
+It is also possible to combine the above into a custom route,
+
+.. code-block:: python
+
+    @blueprint.get("/custom.json")
+    async def custom_openapi():
+        schema = BlueprintOnlyOpenAPIProvider(blueprint.name, current_app, quart_schema).schema()
+        return current_app.json.response(schema)
+
+Please note this assumes the blueprint is not nested as the name will
+be prefixed with the parents blueprint's names.

docs/how_to_guides/index.rst

@@ -7,6 +7,7 @@ How to guides
 
    casing.rst
    configuration.rst
+   customising.rst
    documenting.rst
    error_handling.rst
    headers_validation.rst

src/quart_schema/__init__.py

@@ -15,6 +15,7 @@
     Info,
     License,
     OAuth2SecurityScheme,
+    OpenAPIProvider,
     OpenIdSecurityScheme,
     Server,
     ServerVariable,
@@ -48,6 +49,7 @@
     "Info",
     "License",
     "OAuth2SecurityScheme",
+    "OpenAPIProvider",
     "OpenIdSecurityScheme",
     "operation_id",
     "PydanticDumpOptions",