feature: add withCredentials configuration key (via #5149)

* Add the withCredentials configuration key

It enables passing credentials in CORS requests. e.g. Cookies and
Authorization headers.

* Improve withCredentials documentation

* Add unit tests for the withCredentials config

* Update configuration.md

* Update configuration.md

* only set `withCredentials` Fetch flag if the config value is truthy

there are some workarounds in the wild today that involve setting `withCredentials` on `system.fn.fetch` directly. 

this approach avoids mangling those existing workarounds!

* add more test cases

* Update configs-wrap-actions.js

* Update index.js

src/core/index.js

@@ -51,6 +51,7 @@ module.exports = function SwaggerUI(opts) {
     defaultModelsExpandDepth: 1,
     showExtensions: false,
     showCommonExtensions: false,
+    withCredentials: undefined,
     supportedSubmitMethods: [
       "get",
       "put",

src/core/plugins/swagger-js/configs-wrap-actions.js

@@ -0,0 +1,8 @@
+export const loaded = (ori, system) => (...args) => {
+  ori(...args)
+  const value = system.getConfigs().withCredentials
+  
+  if(value !== undefined) {
+    system.fn.fetch.withCredentials = typeof value === "string" ? (value === "true") : !!value
+  }
+}

src/core/plugins/swagger-js/index.js

@@ -1,4 +1,5 @@
 import Swagger from "swagger-client"
+import * as configsWrapActions from "./configs-wrap-actions"
 
 module.exports = function({ configs, getConfigs }) {
   return {
@@ -22,6 +23,11 @@ module.exports = function({ configs, getConfigs }) {
       },
       serializeRes: Swagger.serializeRes,
       opId: Swagger.helpers.opId
-    }
+    },
+    statePlugins: {
+      configs: {
+        wrapActions: configsWrapActions
+      }
+    },
   }
 }