Refactoring scheduled event to store instant instead of zoned tme zone

[Mehrank64]

The ScheduledEvent class has never preserved the time
zone so it makes more sense for it to store the start and
end time using Instant rather than ZonedDateTime.

Closes #38620

[elasticmachine]

Pinging @elastic/ml-core

[benwtrent]

Jenkins retest this please

[benwtrent]

@Mehrank64 Thank you so much for opening the PR 🚀 . Here are some gradle tasks to see if all the preCommit linting passes and the basic unit tests.

./gradlew :x-pack:plugin:core:preCommit :x-pack:plugin:ml:preCommit :x-pack:plugin:core:test :x-pack:plugin:ml:test

It looks like some linting failures are causing the builds to fail.

[droberts195]

There's a discrepancy here - it's interpreting a millisecond number as seconds, resulting in a time long in the future.

[Mehrank64]

It was definitely a mistake. just solved!

[droberts195]

Regarding the wildcard imports, which the style checker doesn't like, there is advice on how to stop IntelliJ switching to wildcards in https://github.com/elastic/elasticsearch/blob/master/CONTRIBUTING.md:

• IntelliJ: Preferences/Settings->Editor->Code Style->Java->Imports. There are two configuration options: Class count to use import with '*' and Names count to use static import with '*'. Set their values to 99999 or some other absurdly high value.

Hopefully if you change that setting and then re-save the files from IntelliJ it will remove the wildcard imports.

[Mehrank64]

@Mehrank64 Thank you so much for opening the PR 🚀 . Here are some gradle tasks to see if all the preCommit linting passes and the basic unit tests.

./gradlew :x-pack:plugin:core:preCommit :x-pack:plugin:ml:preCommit :x-pack:plugin:core:test :x-pack:plugin:ml:test

It looks like some linting failures are causing the builds to fail.

[Mehrank64]

@benwtrent I did resolve the linting failures and the now all the tests should pass. I closed the PR by accident and can't find any way to re-open it. will raise another PR.

[droberts195]

Jenkins retest this please

[benwtrent]

Jenkins retest this please

[droberts195]

LGTM

Thanks for the contribution @Mehrank64 - much appreciated!