Add bulk operations to subscriber view

I added a basic implementation and one operation "Delete subscriber" for example.

We need to discuss what other operations are needed. Maybe new operations can be done in other tasks so as not to block the current one.

Great I really like the idea.

1) My main concern is that the fix adds a lot of lines of code - and already this module has way too much code to easily maintain. I would like to check if all this code is really necessary, or if there could be a simpler solution. I looked at Core, and I see that Node.php is similar to what you did, but Media and User entities are simpler.

1. SubscriberBulkForm is identical to BulkForm so do we really need it?
2. Media.php doesn't have anything in the routing file, and it uses the default DeleteMultipleForm without overriding. Do we definitely need these parts?
3. Maybe we don't need to alter existing views in the update hook - some sites might even prefer not to have a bulk action.

2) It would be great to have a test of the bulk function.

Thanks