Always return VIP as host if set (#179)

## Issue
We would like to always return the configured VIP as the host when
externally connected (to support use cases where the VIP may be
configured outside of the charms e.g. openstack octavia)

## Solution
Update the conditions that 
1. Report host as configured VIP if externally accessible
2. Set active status on the unit if the charm is the leader and VIP is
configured (and prior compatibility checks run - i.e. charm is
externally accessible when related to hacluster + charm has a VIP if
related to hacluster + VIP is configured only when related to
data-integrator)

## Reference
PGBouncer charm has the above described functionality:
https://github.com/canonical/pgbouncer-operator/pull/337/files#diff-b9ed39bbc9c0387bd3e07da31d13373745534a1cd723d3e292c73496b12e307cR551

Author: shayancanonical

src/charm.py

@@ -97,12 +97,13 @@ def _logrotate(self) -> machine_logrotate.LogRotate:
     def host_address(self) -> str:
         """The host address for the machine."""
         if (
-            self._ha_cluster.relation
-            and self._ha_cluster.is_clustered()
-            and self.config.get("vip")
+            not self.is_externally_accessible(event=None)
+            or not self.config.get("vip")
+            or (self._ha_cluster and not self._ha_cluster.is_clustered())
         ):
-            return self.config["vip"]
-        return str(self.model.get_binding("juju-info").network.bind_address)
+            return str(self.model.get_binding("juju-info").network.bind_address)
+
+        return self.config["vip"]
 
     @property
     def _read_write_endpoints(self) -> str:

src/relations/hacluster.py

@@ -10,8 +10,6 @@
 
 import ops
 
-import workload
-
 HACLUSTER_RELATION_NAME = "ha"
 
 logger = logging.getLogger(__name__)
@@ -36,6 +34,9 @@ def relation(self) -> Optional[ops.Relation]:
 
     def is_clustered(self) -> bool:
         """Check if the related hacluster charm is clustered."""
+        if not self.relation:
+            return False
+
         for key, value in self.relation.data.items():
             if (
                 isinstance(key, ops.Unit)
@@ -57,13 +58,6 @@ def get_unit_juju_status(self) -> ops.StatusBase:
         if vip and not self.charm.is_externally_accessible(event=None):
             return ops.BlockedStatus("vip configuration without data-integrator")
 
-        if (
-            isinstance(self.charm.get_workload(event=None), workload.AuthenticatedWorkload)
-            and self.charm.unit.is_leader()
-            and vip
-        ):
-            return ops.ActiveStatus(f"VIP: {vip}")
-
     def set_vip(self, vip: Optional[str]) -> None:
         """Adds the requested virtual IP to the integration."""
         if not self.relation: