Add verification guide for parquet-java release

[raulcd]

Rationale for this change

There is currently no guide on how to verify. Having a guide will encourage people to verify the release.
This guide should also be linked on the Voting thread.

What changes are included in this PR?

Added documentation about how to verify.

Are these changes tested?

I've validated all steps localy

Closes apache/parquet-java#3091

(Maybe someone with permissions can move that issue to this repo :) )

[wgtmac]

+1 Thanks @raulcd!

cc @gszadovszky @Fokko

[Fokko]

We should probably add the excluded files to a .rat-excludes file: https://github.com/apache/iceberg/blob/main/dev/.rat-excludes

[raulcd]

Yes, I was having some issues integrating the .rat-excludes file with the rat-plugin on my original PR:
https://github.com/apache/parquet-java/pull/3101/files#r1876006229
We might want to do that once we update rat-plugin to use a single source for rat-excludes instead of listing exclusions on the pom.xml?

[wgtmac]

Should we merge this? Do you have any concern? @Fokko

[alamb]

@raulcd shall we merge this PR? Looks like it has been waiting for a while and @wgtmac last asked in Feb.

If we don't hear anything by the end of the year, perhaps we should close this PR (and we can always reopen if/when we want to reconsider)

[raulcd]

Thanks for the ping @alamb , totally forgot about this.
@Fokko had a valid concern. I wasn't able to fix the Java apache-rat pom configuration issue mentioned and didn't have more time for it.
We could:

• merge as is and follow up once we update the rat-plugin
• Update the instructions for license check and leave it as You must check licenses but not give individual steps on how to do it.
• Someone spends some time to try and fix the rat-plugin issue.
• Close the PR. Even though I think there are some nice improvements to the verification guide :)