docs: added documentation on testing tools (#8939)

- Added documentation on how to use Medusa's tools from the `medusa-test-utils` package to create integration and unit tests.
- Added a manual reference on the `medusaIntegrationTestRunner` and `moduleIntegrationTestRunner` functions. Since the typings in the source code aren't very informative, I opted for a manual reference shedding light on the important bits.

Closes DOCS-852

www/apps/book/sidebar.mjs

@@ -370,13 +370,42 @@ export const sidebar = numberSidebarItems(
       children: [
         {
           type: "link",
-          path: "/debugging-and-testing/logging",
-          title: "Logging",
+          path: "/debugging-and-testing/testing-tools",
+          title: "Testing Tools",
         },
         {
           type: "link",
-          path: "/debugging-and-testing/tools",
-          title: "Tools",
+          path: "/debugging-and-testing/testing-tools/integration-tests",
+          title: "Integration Tests",
+          children: [
+            {
+              type: "link",
+              path: "/debugging-and-testing/testing-tools/integration-tests/api-routes",
+              title: "Example: API Routes Tests",
+            },
+            {
+              type: "link",
+              path: "/debugging-and-testing/testing-tools/integration-tests/workflows",
+              title: "Example: Workflows Tests",
+            },
+          ],
+        },
+        {
+          type: "link",
+          path: "/debugging-and-testing/testing-tools/modules-tests",
+          title: "Modules Tests",
+          children: [
+            {
+              type: "link",
+              path: "/debugging-and-testing/testing-tools/unit-tests/module-example",
+              title: "Example",
+            },
+          ],
+        },
+        {
+          type: "link",
+          path: "/debugging-and-testing/logging",
+          title: "Logging",
         },
       ],
     },