app,create-app: migrate to relative tab routes

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

.changeset/flat-walls-kiss.md

@@ -0,0 +1,27 @@
+---
+'@backstage/create-app': patch
+---
+
+Updated the entity page routes to use relative routes rather than absolute ones. This change is required to be able to upgrade to `react-router` v6 stable in the future.
+
+To apply this change to an existing app, update the path prop of `EntityLayout.Route`s to be relative. For example:
+
+```diff
+   <EntityLayoutWrapper>
+-    <EntityLayout.Route path="/" title="Overview">
++    <EntityLayout.Route path="." title="Overview">
+       {overviewContent}
+     </EntityLayout.Route>
+
+-    <EntityLayout.Route path="/ci-cd" title="CI/CD">
++    <EntityLayout.Route path="ci-cd" title="CI/CD">
+       {cicdContent}
+     </EntityLayout.Route>
+
+-    <EntityLayout.Route path="/errors" title="Errors">
++    <EntityLayout.Route path="errors" title="Errors">
+       {errorsContent}
+     </EntityLayout.Route>
+```
+
+This change should also be applied to any other usage of `TabbedLayout`.