[Announcements] Allow announcements to be sent to other targets

### Description

Allow filtering the target of an announcement based on role; this is additional to the existing filtering by the department.

### Test environment

On the Web interface, in an organization's admin interface.

### Preconditions

You need an organization with different departments and roles.

### Steps of Reproduction

1. Go to `/announcements/add` to create a new announcement
2. In the `Target` section, select the target group of the announcement

### Expected Result

There should also be a section with Roles that can be filtered.

### Actual Result

An admin can only select to filter through the departments of the NGO.

### Screenshots