[FLINK-16166][build] Append additional javadoc options

[zentol]

Ensures that additional options can be specified for the javadoc-plugin in profiles/modules.
Without this change the javadoc-plugin configuration in the java 11 profile overrides the doclint option, since the additionalJOptions attribute is an array which are merged by index.

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[tillrohrmann]

Thanks for creating this PR @zentol. LGTM. +1 for merging.