Bootstrap with force (#187)

Instead of relying on the existence of old router user to cleanup router
from cluster metadata, force bootstrap so that the metadata does not
need to be cleaned up.

Fixes canonical/mysql-k8s-operator#345. The
issue was that the router charm would delete the user & router metadata,
but that only the user deletion would go through. Then, on the router
charm's next hook, the bootstrap failed because the metadata was not
cleaned up.

Additional context:
https://chat.canonical.com/canonical/pl/temrphcp3in5xqftkaxgowqtkr

src/workload.py

@@ -153,14 +153,13 @@ def _router_id(self) -> str:
         return f"{socket.getfqdn()}::system"
 
     def _cleanup_after_upgrade_or_potential_container_restart(self) -> None:
-        """Remove Router cluster metadata & user after upgrade or (potential) container restart.
+        """Remove Router user after upgrade or (potential) container restart.
 
         (On Kubernetes, storage is not persisted on container restart—MySQL Router's config file is
         deleted. Therefore, MySQL Router needs to be bootstrapped again.)
         """
         if user_info := self.shell.get_mysql_router_user_for_unit(self._charm.unit.name):
             logger.debug("Cleaning up after upgrade or container restart")
-            self.shell.remove_router_from_cluster_metadata(user_info.router_id)
             self.shell.delete_user(user_info.username)
             logger.debug("Cleaned up after upgrade or container restart")
 
@@ -176,6 +175,7 @@ def _get_bootstrap_command(self, password: str) -> typing.List[str]:
             + ":"
             + self._connection_info.port,
             "--strict",
+            "--force",
             "--conf-set-option",
             "http_server.bind_address=127.0.0.1",
             "--conf-use-gr-notifications",