changesets: added changesets for the new root http router service

Co-authored-by: blam <ben@blam.sh>
Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

.changeset/fair-ants-work.md

@@ -0,0 +1,7 @@
+---
+'@backstage/backend-app-api': minor
+---
+
+**BREAKING**: The `httpRouterFactory` now accepts a `pathPrefix` option rather than `indexPlugin`. To set up custom index path, configure the new `rootHttpRouterFactory` with a custom `indexPath` instead.
+
+Added an implementation for the new `rootHttpRouterServiceRef`.

.changeset/gorgeous-days-applaud.md

@@ -0,0 +1,5 @@
+---
+'@backstage/backend-plugin-api': patch
+---
+
+Added a new `rootHttpRouterServiceRef` and `RootHttpRouterService` interface.

.changeset/tiny-cooks-hide.md

@@ -0,0 +1,5 @@
+---
+'@backstage/backend-defaults': patch
+---
+
+The new root HTTP router service is now installed by default.

packages/backend-app-api/src/services/implementations/rootHttpRouterService.ts

@@ -63,6 +63,9 @@ export const rootHttpRouterFactory = createServiceFactory({
 
     return {
       use: (path: string, handler: Handler) => {
+        if (path.match(/^[/\s]*$/)) {
+          throw new Error(`Root router path may not be empty`);
+        }
         const conflictingPath = findConflictingPath(existingPaths, path);
         if (conflictingPath) {
           throw new Error(