feat: adding support for bastion / jumpbox support

[hugoJuhel]

Objective

The PR aims at adding supports for Jump / Bastions servers to the connector so that connecting to a server behind a VPN would be possible.

Proposed modifications

• The code modifies the way the connection is opened by the adapter.
• If provided with ssh_tunnel_host, ssh_tunnel_port, ssh_tunnel_username and one of either ssh_tunnel_password or ssh_tunnel_ssh_key_path, the adapter first establishes a sshtunnel to the jump host before connecting to the server.
• The code uses sshtunnel to handles the tunnel creation.
• A dataclass is introduced to bind the pyodbc.Connection.close method to the SSHTunnelForwarder.close method.
• The dataclass is preferred over registering a callback in pyodbc since pyodbc.close attribute is not settable.

[sdebruyn]

Should be rebased on current master so that there are no formatting changes anymore

[hugoJuhel]

@sdebruyn Hi,

I have just pushed a commits with everything rebased on master.

hj

[sdebruyn]

I'm not sure support for SSH tunneling should be a feature of this adapter that we would want to maintain, as well as an extra dependency that would not be needed for 99% of the users. Closing this for now.