rejoin-instance action should have "address" parameter mandatory

Currently it's possible to run "rejoin-instance" action without specifying "address" parameter, resulting in following error:

unit-mysql-innodb-cluster-0:
  UnitId: mysql-innodb-cluster/0
  id: "14"
  message: Rejoin instance failed
  results:
    output: "Cannot set LC_ALL to locale en_US.UTF-8: No such file or directory\n\e[31mERROR:
      \e[0mUnable to connect to the target instance 'None'. Please verify the connection
      settings, make sure the instance is available and try again.\nTraceback (most
      recent call last):\n File \"<string>\", line 3, in <module>\nmysqlsh.DBError:
      MySQL Error (2005): Cluster.rejoin_instance: Could not open connection to 'None':
      Unknown MySQL server host 'None' (11)\n"
    traceback: |
      Traceback (most recent call last):
        File "/var/lib/juju/agents/unit-mysql-innodb-cluster-0/charm/actions/rejoin-instance", line 231, in rejoin_instance
          output = instance.rejoin_instance(address)
        File "/var/lib/juju/agents/unit-mysql-innodb-cluster-0/charm/lib/charm/openstack/mysql_innodb_cluster.py", line 938, in rejoin_instance
          raise e
        File "/var/lib/juju/agents/unit-mysql-innodb-cluster-0/charm/lib/charm/openstack/mysql_innodb_cluster.py", line 926, in rejoin_instance
          output = self.run_mysqlsh_script(_script).decode("UTF-8")
        File "/var/lib/juju/agents/unit-mysql-innodb-cluster-0/charm/lib/charm/openstack/mysql_innodb_cluster.py", line 1659, in run_mysqlsh_script
          return subprocess.check_output(cmd, stderr=subprocess.PIPE)
        File "/usr/lib/python3.8/subprocess.py", line 415, in check_output
          return run(*popenargs, stdout=PIPE, timeout=timeout, check=True,
        File "/usr/lib/python3.8/subprocess.py", line 516, in run
          raise CalledProcessError(retcode, process.args,
      subprocess.CalledProcessError: Command '['/snap/bin/mysqlsh', '--no-wizard', '--python', '-f', '/root/snap/mysql-shell/common/tmp3z92uc2y.py']' returned non-zero exit status 1.
  status: failed