Note on Backup Entry Processor usage

EntryProcessor interface returns "this" instance as the default backup entry processor.
So, all the business logic of the primary entry processor ("this") is carried to the backup and causes unnecessary execution.

We can drop a note to the documentation and tell the users that they can just carry the computed value and update the backup entry. This way, they'll avoid running unnecessary business logic to reach to the same computed value.

Another important note on Offloadable Entry Processors;

Even though Offloadable EPs run on its own executor, its backup EPs run on partition threads.
We can mention this design too, which adds to the importance of the first point.

Locate the documentation sections covering EntryProcessor and Offloadable Entry Processors. Read the existing guidance, then add notes about the default backup processor behavior and that offloaded backup processors run on partition threads. Done means users can identify when to carry only the computed value and understand the backup execution context.

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