[RAM] Make the Cancel Snooze button skip the current recurrence

[Zacqary]

Summary

Part of #132860. This updates the backend to allow the Cancel Snooze button to skip the currently active recurrence of a snooze, while keeping future recurrences of that snooze schedule intact.

This does NOT incorporate the UI changes in #132860. These will merge in a later PR.

To test

• Schedule a snooze that starts NOW and recurs every day/week/etc
• Refresh the page, press the Cancel Snooze button
• Ensure that the current snooze is cancelled but the snooze schedule still exists

Checklist

• Unit or functional tests were updated or added to match the most common scenarios

[elasticmachine]

Pinging @elastic/response-ops (Team:ResponseOps)

[JiaweiWu]

LGTM

[Zacqary]

@elasticmachine merge upstream

[kibana-ci]

💚 Build Succeeded

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id	before	after	diff
alerting	356	357	+1

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id	before	after	diff
alert	74	75	+1

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API count

id	before	after	diff
alerting	365	366	+1

History

• 💚 Build #57894 succeeded 25b2d8a
• 💚 Build #57856 succeeded 81a2093

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@elasticmachine merge upstream