SAK-48874 Assignments implementation of Interface HardDeleteAware

[jkjanetschek]

This implementation is using the Interface HardDeleteAware. Only data which concerns the tool is considered.

[jkjanetschek]

This PR is related to PR SAK-48874 Assignments support removal of data when site is hard deleted #11547
https://github.com/sakaiproject/sakai/pull/11547

[ern]

Hi @jkjanetschek, I looked this over and will add the missing bits to the other PR.

One thing I noticed while looking at this, is interfaces like HardDeleteAware are not designed and implemented properly.
The design is that the entity (object) broker system should be responsible for calling notifying it's entities that something is occurring and action should be taken by the affected entities, in this case a site is being removed so the related entities should be removed. However It should be the responsibility of the EntityManager to initiate the appropriate action (EntityManager would need to be informed that such an action is happening likely by the SiteRemovalAdvisor).

So in the end a few adjustments will be needed to properly reflect this chain of command.

Thank you for pointing this out!