[DOCS] Auto-tuning the date-time picker for event analyzer

[nastasha-solomon]

Description

In 8.5, the visual event analyzer automatically includes the entire process tree if a user tries to examine a timeframe (or part of the tree?) that has 0 process events in it. In addition, the user will be given a notice that events exist in a different time frame and a recommendation to adjust their selected time frame. The rec displays in the form of a toast message.

Related issues/PRs

• https://github.com/elastic/security-team/issues/2210
• [Security Solution] Make timerange an optional request param, fire unbounded request when 0 results kibana#140831

Notes

• If a user supplies a time range that results in 0 events, the request is retried without any time range at all. If the retry results in 1 or more event, that's shown that in analyzer. If there are still no events, the same empty message (the toast?) displays.
• Might need to explain the results of the autotuning in Visual event analyzer docs.

[nastasha-solomon]

Verified with @kqualters-elastic that can doc this enhancement in release notes only. Users might not encounter this functionally often. It only kicks in during the rare case that a user selects a time/date range without any events.
cc: @jmikell821 @benironside

[nastasha-solomon]

Closing as this is doc'd in #2519.