Merge pull request #13574 from backstage/rugvip/testroot

cli: add repo test command and start running tests from the root

.changeset/little-roses-rule.md

@@ -0,0 +1,5 @@
+---
+'@backstage/cli': patch
+---
+
+Added a new `repo test` command.

.changeset/tiny-mails-bathe.md

@@ -0,0 +1,14 @@
+---
+'@backstage/create-app': patch
+---
+
+Updated the root `test` scripts to use `backstage-cli repo test`.
+
+To apply this change to an existing app, make the following change to the root `package.json`:
+
+```diff
+-    "test": "backstage-cli test",
+-    "test:all": "lerna run test -- --coverage",
++    "test": "backstage-cli repo test",
++    "test:all": "backstage-cli repo test --coverage",
+```