1) github.com/jtblin/go-ldap-client is an abandoned project and not keeping
up with go modules, so pull that code in (single file, BSD license)
2) minor refactor ldap as a result of 1)
3) update go.mod
I just did a fresh 'make' of zot, and it generated these changes to go.mod
and go.sum; let's include them.
Signed-off-by: Tycho Andersen <tycho@tycho.ws>