v5.38.0 Changelog (#4810)

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Co-authored-by: Carrie Warner (Mattermost) <74422101+cwarnermm@users.noreply.github.com>

* Update self-managed-changelog.md

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Co-authored-by: Carrie Warner (Mattermost) <74422101+cwarnermm@users.noreply.github.com>