Add ability to make each alert visible to selected role(s)

Fixes should be in MR.

a.dmitriiev → made their first commit to this issue’s fork.

I have created a MR based on the changes from the previous patches. I had to do some modifications, as the patches were for module version 2.x. Also instead of list field type I am using entity reference field type for Roles selection and also the check is now on query level, so query selects all alerts that do not have role restrictions or it is for the roles that current user has.

I think that adding cache context user.roles should exactly make sure that the cached alerts will be served to correct users. Do we really need a test for this?

Attaching the patch also, so that it can be used with composer patches version 2, as it doesn't allow patches from MRs.