Allow an organization to select their preferred channel for notifications

[shemogumbe]

As an organization's administrator, one should be able to select the preferred channel for notification upon actions on data requests to the organizations. These should be after a data request is created, commented on, and after the status of a data request has changed.

[WNjihia]

Assigned to @WNjihia and @ignatius

[ignatiusukwuoma]

The PR for this issue is available @DavidLemayian