GH-3089: Add missing license header to pom.xml

[raulcd]

Rationale for this change

The license header is missing as reported on the release vote thread.

What changes are included in this PR?

Adding the missing header. It has been copied from parquet-java/parquet-cli/pom.xml

Are these changes tested?

Via CI

Are there any user-facing changes?No

Closes #3089

[raulcd]

@Fokko FYI

[raulcd]

The CI failure for Build Parquet with JDK 11 and gzip,snappy is not related but I seem to have seen that failure on other PRs, places like the 1.15.0 branch: https://github.com/apache/parquet-java/actions/runs/12075877527/job/33676391448
I don't seem to find an issue to track the flaky issue, I can open one.

[wgtmac]

Thanks @raulcd! I've re-triggered the failed test.

[Fokko]

Thanks for adding this @raulcd, this seems to be the only pom.xml with the missing header.