Refactor the nowInMillisResolution in a common place

[pgomulka]

depending on the underlying hardware and the JVM version the Clock.system(zone) can return a time with different resolution. ZonedDateTime is using that under the hood
This was changed from in jdk>8
We are already doing this in watcher, ML, sql tests. Worthy to extract in a single place.

sql https://github.com/elastic/elasticsearch/pull/36877/files
watcher #38405
ml #38506

[elasticmachine]

Pinging @elastic/es-core-infra