Merge branch 'docs-add-memory-metadata' into 'master'

Add Memory metadata to Sidekiq memory killer page

See merge request gitlab-org/gitlab!46462

doc/administration/operations/sidekiq_memory_killer.md

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-stage: none
-group: unassigned
+stage: Enablement
+group: Memory
 info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
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