Permission field validation in Create Group API

[anshsrtv]

Is your feature request related to a problem? Please describe.

A field level validation for permission_array field in [post] /api/org/(org-id)/group/ API instead of using the CreateGroupSerializer.permissions_valid(). As asked in comment in #110

The function below has to be replaced and can be used as a reference:

def permissions_valid(self):
    self.perm = Permissions()
    try:
        self.perm.set_permissions(
            permissions_array=self.initial_data['permissions_array']
        )
    except PERMISSION_INT_INVALID as perm_int_invalid:
        self._errors["permissions_array"]=str(perm_int_invalid)
    else:
        self._errors = {}
    return not bool(self._errors)

Describe the solution you'd like

Instead of using CreateGroupSerializer.permissions_valid(), use Field-level validation to let serializer.is_valid() do the validation of permission_array.

Describe alternatives you've considered

Use the Permissions.set_permissions() of custom_model_field.py to validate the permission ints in the permission_array using try except else statement. Catch the PERMISSION_INT_INVALID exception in the except clause.

Additional context

The reference for the solution can be Field-level validation

[harshakhmk]

I would like to work on this issue @anshsrtv