Feature 10887: Add cross-model relations support

Changes:
- Extend `add_relation` method in N2VCJujuConn to include the CMR case
- Add `add_relation` method to K8sJujuConn
- Add n2vc/definitions.py file that includes definition ofjects for
Offer and RelationEndpoint.
- Change `n2vc.libjuju.Libjuju.list_offers` method to be private, and accept a filter `offer_name` parameter.
- Update `n2vc.libjuju.Libjuju.consume` method arguments.
- Add `n2vc.libjuju.Libjuju.offer` method to create an offer.

Unit tests associated to the code changes have been either created or
updated accordingly

Change-Id: Ibf8d574528dee0fa898e0e97578dd3a6aa68316a
Signed-off-by: David Garcia <david.garcia@canonical.com>
diff --git a/n2vc/tests/unit/test_utils.py b/n2vc/tests/unit/test_utils.py
index bffbc29..3896b2f 100644
--- a/n2vc/tests/unit/test_utils.py
+++ b/n2vc/tests/unit/test_utils.py
@@ -14,7 +14,13 @@
 
 from unittest import TestCase
 
-from n2vc.utils import Dict, EntityType, JujuStatusToOSM, N2VCDeploymentStatus
+from n2vc.utils import (
+    Dict,
+    EntityType,
+    JujuStatusToOSM,
+    N2VCDeploymentStatus,
+    get_ee_id_components,
+)
 from juju.machine import Machine
 from juju.application import Application
 from juju.action import Action
@@ -84,3 +90,17 @@
                 osm_status = status["osm"]
                 self.assertTrue(juju_status in JujuStatusToOSM[entity_type])
                 self.assertEqual(osm_status, JujuStatusToOSM[entity_type][juju_status])
+
+
+class GetEEComponentTest(TestCase):
+    def test_valid(self):
+        model, application, machine = get_ee_id_components("model.application.machine")
+        self.assertEqual(model, "model")
+        self.assertEqual(application, "application")
+        self.assertEqual(machine, "machine")
+
+    def test_invalid(self):
+        with self.assertRaises(Exception):
+            get_ee_id_components("model.application.machine.1")
+        with self.assertRaises(Exception):
+            get_ee_id_components("model.application")