v3 docs: Add updated_ats filter for audit events

[#173691526](https://www.pivotaltracker.com/story/show/173691526)

Co-authored-by: Merric De Launey <mdelauney@pivotal.io>
Co-authored-by: Reid Mitchell <rmitchell@pivotal.io>

Author: MerricdeLauney

docs/v3/source/includes/concepts/_filters.md.erb

@@ -48,8 +48,7 @@ This will return all routes with hostname `"hostname1"`, `""` OR `"hostname2"`.
 
 #### Relational Operators (Experimental)
 
-Fields can be filtered using relational operators when listing resources. Currently, this is
-supported only on the `created_at` field, using the `created_ats` filter.
+Fields can be filtered using relational operators when listing resources.
 
 For example, a response to `/v3/audit_events?created_ats[lt]=2020-06-30T12:34:56Z` will contain
 audit events with a `created_at` timestamp strictly earlier than `2020-06-30T12:34:56Z`.

docs/v3/source/includes/resources/audit_events/_list.md.erb

@@ -31,6 +31,7 @@ Retrieve all audit events the user has access to.
 Name | Type | Description
 ---- | ---- | ------------
 **created_ats** (*experimental*)| _[timestamp](#timestamps)_ | Timestamp to filter by. When filtering on equality, several comma-delimited timestamps may be passed. Also supports filtering with [relational operators](#relational-operators-experimental)
+**updated_ats** (*experimental*)| _[timestamp](#timestamps)_ | Timestamp to filter by. When filtering on equality, several comma-delimited timestamps may be passed. Also supports filtering with [relational operators](#relational-operators-experimental)
 **types** | _list of strings_ | Comma-delimited list of event types to filter by
 **target_guids** | _list of strings_ | Comma-delimited list of target guids to filter by
 **space_guids** | _list of strings_ | Comma-delimited list of space guids to filter by