Update CHANGELOG-EE.md for 13.11.0-ee

[ci skip]

ee/changelogs/unreleased/sy-support-arrays-in-custom-mappings.yml

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-title: Add support for array indexing to alert integration custom mappings
-merge_request: 58610
-author:
-type: added

ee/changelogs/unreleased/threat-monitoring-policy-editor-source-editor.yml

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-title: 'Policy Editor: switching the custom editor to Source Editor'
-merge_request: 57508
-author:
-type: changed

ee/changelogs/unreleased/tr-oncall-schedule-fix-width-calc.yml

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-title: Fix the oncall schedule timeline width calc
-merge_request: 58973
-author:
-type: fixed

ee/changelogs/unreleased/tr-oncall-schedule-reduce-daily-query.yml

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-title: Reduce query timespan to one day in schedule daily view
-merge_request: 58974
-author:
-type: fixed

ee/changelogs/unreleased/ui-text-incidents.yml

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-title: Updated UI text to match style guidelines
-merge_request: 58509
-author:
-type: other

ee/changelogs/unreleased/use-copyable_field-in-issue-email.yml

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-title: Adjust Button Size on License Compliance widget
-merge_request: 57592
-author:
-type: fixed

ee/changelogs/unreleased/vij-billable-count-gql.yml

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-title: Add billable_members_count to GraphQL Group type
-merge_request: 57712
-author:
-type: changed

ee/changelogs/unreleased/vsa-fix-update-empty-vsa.yml

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-title: Fix updating value stream without persisted stages
-merge_request: 59176
-author:
-type: fixed