chore: Extract sidebar item injection token into separate package

- Add unit tests to cover custom resources sidebar items

Signed-off-by: Sebastian Malton <sebastian@malton.name>

packages/cluster-sidebar/.eslintrc.js

@@ -0,0 +1,6 @@
+module.exports = {
+    extends: "@k8slens/eslint-config/eslint",
+    parserOptions: {
+      project: "./tsconfig.json",
+    },
+  };