Update CSP MP docs to cover incomplete registration for signup

[aashishkohli]

As part of MP subscription and sign up process customers have to redirect to CH Cloud and sign up once they have subscribed on the CSP MP. Sometimes customers subscribe on the MP portal but do not complete the redirect to CH Cloud and signup process. They are then left wondering what happened with their subscription.

We need to include an FAQ or error scenario note in the main flow to cover this situation.