Alert configuration roles array should not be required

[themantissa]

Provider version 0.5.0

Issue:
The MongoDB Atlas documentation states that notifications.roles is required, when it is not (see https://docs.atlas.mongodb.com/reference/api/alert-configurations-create-config/) a request will be submitted to correct the docs bug. However roles really only applies if the notification type is GROUP, and even then when omitted it simply sends the alert to all users in the project. Currently requiring roles is likely to break alert configs set to EMAIL, which does not need roles.

[themantissa]

@PacoDw should hopefully be a quick fix.

[themantissa]

FYI to others 0.4.2 does not have this issues so if you upgraded to 0.5.0, please downgrade till this is addressed.