release: v4.0.0 - bring nearcore 2.0.0 protocol breaking changes

[frol]

The main breaking change is the maximum size of transactions which went from 4.2MB down to 1.5MB. It is safer to release it as 4.x series than risking breaking the users code. Overall, 4.0.0 release upgrade should be smooth for 3.x users.

[frol]

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