HTCONDOR-1011 Add docs for dealing with _ in credential names
HTCONDOR-1011 Add docs for dealing with _ in credential names

Also added explainer specific for OAuth users.

htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor