SOLR-18070 Add more changelog checks to smoke tester

[janhoy]

Adds checks to smoke tester

• folder changelog/unreleased is empty
• folder changelog/v{releaseVer} exists and does not contain a release-date.txt
• other changelog/vx.y.z folders do contain a release-date.txt
• validate that generated Changes.html does not list a release-date for current release

The new tests run by default, but can be disabled with new --skip-changelog-current option. This allows e.g. Jenkins to run smoke tester a week before the RM starts generating final changelog, i.e. the smoke tester will then accept that unreleased folder contains files...

https://issues.apache.org/jira/browse/SOLR-18070

[github-actions]

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[dsmiley]

What's the status here?

[janhoy]

What's the status here?

Status is that the added checks look good, they will validate that changelog in the release-artifacts are as expected.

But to also be able to run the smokeTester a week or two before the release starts, and before the RM generates CHANGELOG.md, I have added a new cli flag --skip-changelog that we can pass in Jenkins, which will skip those extra deep changelog checks.