fix: entity to be Partial<Entity> | undefined in UpdateEvent

[francescoferraioli]

Description of change

This change was requested as part of #7724.

That change has made us realise that the type of UpdateEvent.entity is not strictly correct as just Entity.

1. The UpdateEvent in case of an update, the entity was undefined

• In fix: entity object undefined in update subscriber #5443 this was changed for beforeUpdate to be a Partial
• In fix: entity object undefined in afterUpdate subscriber #7724 this will be changed for afterUpdate to be a Partial<Entity>

2. The UpdateEvent in case of a soft delete, the entity is undefined

• There is no PR to try and update this

This PR corrects the type for all scenarios which is entity: Partial<Entity> | undefined.

I decided to split this out into a seperate PR from #7724 for a number of reasons:

• The correctness of the type spans more than just the afterUpdate subscriber
• It is a change in the API and is thus a breaking change, whilst fix: entity object undefined in afterUpdate subscriber #7724 is not.

Pull-Request Checklist

• Code is up-to-date with the master branch
• npm run lint passes with this change
• npm run test passes with this change
• This pull request links relevant issues as Fixes #0000 (N/A)
• There are new or updated unit tests validating the change (N/A)
• Documentation has been updated to reflect this change (N/A)
• The new commits follow conventions explained in CONTRIBUTING.md

[francescoferraioli]

Thanks for approving @imnotjames. It looks like I don't have permission to merge this PR in. Is it something you do after approving?