backend-plugin-api: added new core identity service

Co-authored-by: Johan Haals <johan.haals@gmail.com>
Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

.changeset/flat-toes-repair.md

@@ -0,0 +1,5 @@
+---
+'@backstage/backend-defaults': patch
+---
+
+Added factory for the new core identity service to the set of default service factories.

.changeset/forty-chairs-judge.md

@@ -0,0 +1,5 @@
+---
+'@backstage/backend-app-api': patch
+---
+
+Added service factory for the new core identity service.

.changeset/moody-waves-cover.md

@@ -0,0 +1,5 @@
+---
+'@backstage/backend-plugin-api': patch
+---
+
+Added new core identity service.