Migration guide and documentation update [DATAES-750]

[spring-projects-issues]

sothawo opened DATAES-750 and commented

the changes - especially breaking ones - need to be documented and addressed in a migration guide for version 4.0

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Referenced from: pull request #444

[spring-projects-issues]

sothawo commented

@Mark Paluch: where do we put this? As a section in the reference documentation?