Enrollment flow choose COU from URL query string parameter

The proposal is that an enrollment flow with a COU enrollment attribute be able to consume the value for the COU through a URL query string parameter.

The idea is to allow a deployer to construct a URL for a given organization corresponding to the COU and share it with the enrollees. When the enrollees  from that organization enroll they will not have to choose their COU (since the users often get it wrong). 

Currently this can only be accomplished by configuring a separate enrollment flow for each COU and making the COU value be a hidden default, but that results in a large number of enrollment flows which can be difficult to manage and sustain.