update service principals redirect

Author: meirish

content/hcp-docs/redirects.jsonc

@@ -59,6 +59,11 @@
     "destination": "/hcp/docs/hcp/iam/service-principal",
     "permanent": true,
   },
+  {
+    "source": "/hcp/docs/hcp/iam/service-principals",
+    "destination": "/hcp/docs/hcp/iam/service-principal",
+    "permanent": true,
+  },
   {
     "source": "/hcp/docs/hcp/security/sso",
     "destination": "/hcp/docs/hcp/admin/iam/sso",