Add LDAP login error logs

[nfantone]

I was trying to get Homer to work with LDAP authentication, but kept silently failing for me. I noticed there were barely any error or debug logs for most points of failure following the LDAP login flow - which leaves users pretty much in the dark when debugging these sort of issues. Adding a bunch of them help me troubleshoot a config mistake: had a minor typo in my ldap_config.base setting.

This may help others experiencing the same.

[CLAassistant]

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[adubovikov]

Thank you!