Breaking: #68890 - Remove dual-use of auth_timeout_field in AbstractUserAuthentication

See forge#68890


In AbstractUserAuthentication class the property auth_timeout_field could previously either contain the name of a field or a timeout-value in seconds. To specify a field name the property can be used as before. To specify a timeout-value, a new property called sessionTimeout is introduced that can be set to an integer >= 0.


If some extension reads the value, the default is changed from an integer (0) to an empty string.


Extensions modifying auth_timeout_field to a numeric value should switch to using sessionTimeout.