What this PR changes/adds

Avoid infinite loop in DataPlaneManager

How:

• separate transfer "validation" and "transfer", because the retry mechanism on starting a transfer should work only on validation, once the transfer is started, it makes no sense to retry running automatically, because it could fail after some time and this definitely needs to be managed at an higher level
• by doing that, the entityReload feature added on the ProcessRetry becomes unnecessary because the "completion" handling happens outside of the retry loop, so it has been removed altogether
• since the TransferService validation returns a Result and not a StatusResult, the Process implementations have been changed to make them accept every result type that extends AbstractResult
• removed the Boolean type from the result type of the validation, as it was never evaluated. when the result is successful it means that the validation went through, if it is failed, well... :)

Why it does that

fix bug

Further notes

• removed TransferProcessHttpClientIntegrationTest for different reasons:
  • they were testing something that's already well covered e2e
  • they were over complicated
  • they were actually not testing the HTTP client, but the embedded one 🥹
• added callback-static-endpoint module to the bom, I feel like it slipped out

Who will sponsor this feature?

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Linked Issue(s)

Closes #4874

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