sftpgo-ldap v0.4

Primarily added some additional logging calls in, along with some adjustments to how the LDAP connections are made.

The changes related to the LDAP connections aren't as important for this repository, but they were important for the sftpgo-ldap-http-server repository, since that process is long-lived, the fact that I wasn't disconnecting from the LDAP connections was providing to be problematic (which isn't as big of an issue for the normally short-lived web or CLI requests made via the code in this repository).

Now, the code will disconnect from the LDAP connections properly after the authentication attempts are made.