Add intercept of config.json (#10908)

* Add intercept of `config.json`

To help make sure that we run our tests against a known config, rather than
accidentally making requests to `matrix.org`.

* Remove now-redundant stubs of matrix.org files

Now that we intercept config.json, all this stuff is redundant.

* Reinstate fixture which is actually used

Turns out this is used after all

* Add a `map_style_url`

* disable failing axe check

cypress/support/config.json.ts

@@ -0,0 +1,41 @@
+/*
+Copyright 2023 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+/* Intercept requests to `config.json`, so that we can test against a known configuration.
+ *
+ * If we don't do this, we end up testing against the Element config for develop.element.io, which then means
+ * we make requests to the live `matrix.org`, which makes our tests dependent on matrix.org being up and responsive.
+ */
+
+const CONFIG_JSON = {
+    // This is deliberately quite a minimal config.json, so that we can test that the default settings
+    // actually work.
+    //
+    // The only thing that we really *need* (otherwise Element refuses to load) is a default homeserver.
+    // We point that to a guaranteed-invalid domain.
+    default_server_config: {
+        "m.homeserver": {
+            base_url: "https://server.invalid",
+        },
+    },
+
+    // the location tests want a map style url.
+    map_style_url: "https://api.maptiler.com/maps/streets/style.json?key=fU3vlMsMn4Jb6dnEIFsx",
+};
+
+beforeEach(() => {
+    cy.intercept({ method: "GET", pathname: "/config.json" }, { body: CONFIG_JSON });
+});