Provide support for GetFieldMapping request

[ffaoudi]

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Closes #1641

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[sothawo]

thanks for the PR, nice work. There's nothing to object, just some minor things

[ffaoudi]

Hi @sothawo Thanks for the review, I have a question about the version, in the javadoc I put since 4.2, is that correct?

[sothawo]

yes, 4.2 is correct.