Ability to alter default tags for an entity

Problem/Motivation

I'm interested in a feature that was previously implemented in 7.x-1.x but has not been ported to 8.x-1.x and 2.x. It's about this issue #2720723: Add hook to alter instance name for entity config → . I have the same use case - tags per user role.

Proposed resolution

I see two possible solutions:

1. A new hook, for example, hook_metatags_defaults_alter(). This hook must be called inside metatag_get_default_tags(). Probably inside \Drupal\metatag\MetatagManager::defaultTagsFromEntity() too.
2. Port feature from #2720723: Add hook to alter instance name for entity config → to 2.x.

Remaining tasks

1. Consider the possibility of implementation.
2. Choose a solution from the above.
3. Implement.