Allow defining a Role fixed end date

[joaofilipedg]

When we create a Role, the Superuser/Admin can define the Role expiration period (number of days). This is a period that the user will have access to the role, starting from the moment the invitation is accepted.

Although this is useful in many cases, there are situations where an Admin may want Role access to end on a specific date. For example, I could create a role that should give access to an application until the 31st of December, regardless of whether the people accept the invitation in January, in July or on the 25th of December.

A nice feature would be to get this option when creating a Role of defining a fixed Role expiration date? This would probably be incompatible with the Role expiration period (only one of those could be defined).