James Rodewig e46bb54c7b
[DOCS] Document any keyword in EQL syntax (#52821) (#53157)
Adds documentation for the `any` keyword to the EQL syntax docs.

Includes:

* Definition of an event category and its relationship to the event
   category field.
* Example matching all event categories using `any` keyword
* Example using `any` with `where true`
2020-03-05 05:02:47 -05:00
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