Convert Purge plugins to attributes

Problem/Motivation

As per https://www.drupal.org/node/3395582 not providing an attribute class is deprecated in 11.2

If we raise the minimum supported version to 10.2 then we can safely remove the annotations.

Steps to reproduce

N/A

Proposed resolution

Add attribute support

Remaining tasks

Do it

User interface changes

N/A

API changes

Annotations removed, attributes added.

Data model changes

N/A