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/utils.py b/n2vc/utils.py
index 0dbd71e..a661e05 100644
--- a/n2vc/utils.py
+++ b/n2vc/utils.py
@@ -22,6 +22,7 @@
 from juju.action import Action
 from juju.unit import Unit
 from n2vc.exceptions import N2VCInvalidCertificate
+from typing import Tuple
 
 
 def base64_to_cacert(b64string):
@@ -147,3 +148,18 @@
     yaml_text = obj_to_yaml(obj)
     # parse to dict
     return yaml.load(yaml_text, Loader=yaml.Loader)
+
+
+def get_ee_id_components(ee_id: str) -> Tuple[str, str, str]:
+    """
+    Get model, application and machine components from an execution environment id
+    :param ee_id:
+    :return: model_name, application_name, machine_id
+    """
+    parts = ee_id.split(".")
+    if len(parts) != 3:
+        raise Exception("invalid ee id.")
+    model_name = parts[0]
+    application_name = parts[1]
+    machine_id = parts[2]
+    return model_name, application_name, machine_id