Answering the question you asked, no it's not possible to configure a default password in an ssh config file.
But if indeed, as you say, it's "because sometimes I stand away from the PC and when I go back, type a password and press Enter the terminal says CONNECTION CLOSED", then why not prevent closing the session instead? SSH can keep connections alive for you.
Host Home User netmoon Port 22 HostName test.com ServerAliveInterval 300 ServerAliveCountMax 2