Currently, it is quite opaque when Warpgate fails to authenticate with an SSH target (So this is talking about the Warpgate -> Target SSH connection and not the Client -> Warpgate SSH connection). The following happens:

• A message Auth failed is printed to the log
• No message is printed to the user

This can be both hard to understand when you're initially experimenting/setting up Warpgate and make mistakes with authentication, and creates a suboptimal user experience when a user of Warpgate SSHes into the VM and then accidentally deletes the public key of the Warpgate user (which unfortunately happens a bit too often with our users).

This MR makes the following changes:

• Expand log message given in admin logs when this happens
• Add specific message for authentication request failure to print to the user, as it's currently just printed as a generic "Connection Failed"
• Add a small timeout before disconnecting the client as printed error messages are never received by the user, since their session gets disconnected before the message is sent, which means they never receive the message

This is how it looks to the user when warpgate cannot connect to the SSH target now:

Resolves #1667