updates especially when deleting one since we require all sorts of Ids from the object but the object will be deleted by the time
the request reaches other servers so instead we create a json payload to send to other servers which contains all information necessary
to refresh/clear the cache on the other servers. This will probably be the preferred way going forward to handle cache refreshing.
With this in place, when removing a conent type cache is removed based on events.
This also adds a 'class' generic argument constraint to the repository base classes to guarantee we can do null checks and then we also
fix a null check on RepositoryBase. Updates the Entity class to properly support tracking properties - this now allows us to determine if
an entity was new, which is now used to ensure we don't re-update all of the content cache when a new content type is created.
Have also changed the deletion and creation of document types to use the new API, this allows for a lot less processing and streamlining how
all cache is invalidated. Fixes the construction of a new Template and Content Type in the v6 api and ensures that default values are set - #U4-1972, #U4-1971
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