NIFI-7108 - Upgrade com.puppycrawl.tools:checkstyle

[pvillard31]

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Enables X functionality; fixes bug NIFI-YYYY.

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[alopresto]

Thanks Pierre. Looks good to me. +1, merging.

[alopresto]

Building locally on Java 11 to verify.

[alopresto]

Verified the full build locally on Java 11. The Travis thing was a false positive. Merging.