Fix broken links in documentation (#10180)

changelog.d/10180.doc

docs/admin_api/README.rst

docs/admin_api/delete_group.md

docs/admin_api/event_reports.md

docs/admin_api/media_admin_api.md

docs/admin_api/purge_history_api.md

docs/admin_api/room_membership.md

docs/admin_api/rooms.md

docs/admin_api/statistics.md

docs/admin_api/user_admin_api.md

docs/consent_tracking.md

docs/federate.md

docs/message_retention_policies.md

docs/metrics-howto.md

docs/presence_router_module.md

docs/reverse_proxy.md

docs/sso_mapping_providers.md

docs/systemd-with-workers/README.md

docs/workers.md