**Apache Airflow version**: 2.0.2 (but problem can still be found in master)

**What happened**:

When using the SSHHook to connect to an ssh server on a non default port, the host_key setting is not added with the correct hostname to the list of known hosts. In more detail:

```python
from airflow.providers.ssh.hooks.ssh import SSHHook
import paramiko
from base64 import decodebytes

hook = SSHHook(remote_host="1.2.3.4", port=1234, username="user")
# Usually, host_key would come from the connection_extras, for the sake of this example we set the value manually:
host_key = "abc" # Some public key
hook.host_key = paramiko.RSAKey(data=decodebytes(host_key.encode("utf-8")))
hook.no_host_key_check = False

conn = hook.get_conn()
```

This yields the exception

    paramiko.ssh_exception.SSHException: Server '[1.2.3.4]:1234' not found in known_hosts

**Reason**:
In the SSHHook the host_key is added using only the name of the remote host. 
https://github.com/apache/airflow/blob/5bd6ea784340e0daf1554e207600eae92318ab09/airflow/providers/ssh/hooks/ssh.py#L221

According the the known_hosts format, we would need 

```python
hostname = f"[{self.remote_host}]:{self.port}" if self.port != SSH_PORT else self.remote_host
```

**Anything else we need to know**:

I will prepare a PR that solves the problem.

airflow/providers/ssh/hooks/ssh.py
if self.password:
            password = self.password.strip()
            tunnel_kwargs.update(
                ssh_password=password,
            )
        else:
            tunnel_kwargs.update(
                host_pkey_directories=[],
            )
        client = SSHTunnelForwarder(self.remote_host, **tunnel_kwargs)
        return client
    def create_tunnel(
        self, local_port: int, remote_port: int, remote_host: str = "localhost"
    ) -> SSHTunnelForwarder:
        """
        Creates tunnel for SSH connection [Deprecated].
        :param local_port: local port number
        :param remote_port: remote port number
        :param remote_host: remote host
        :return:
        """
        warnings.warn(
            'SSHHook.create_tunnel is deprecated, Please'
            'use get_tunnel() instead. But please note that the'
            'order of the parameters have changed'
            'This method will be removed in Airflow 2.0',
            category=DeprecationWarning,
        )
        return self.get_tunnel(remote_port, remote_host, local_port)
    def _pkey_from_private_key(self, private_key: str, passphrase: Optional[str] = None) -> paramiko.PKey: