lib/log: only log err.Error() for error fields

Created by: bobheadxi

zap.NamedError dives deep into an error to get additional information out, e.g. getting Errors() []error and applying fmt.Stringer. In lib/error a core assumption is that .Error() should provide most important information, so for now we replace the underlying implementation that simply logs a string so that we don't get very noisy output

Test plan