docs: add new param activation deadline in the config file

Summary

• docs: add new param activation deadline in the config file

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• Close docs#489 (closed)

• Cherry-pick to: none

• Follow-up for !1736 (merged)

• Staging:

  • https://docs.binary.picodata.io/picodata/vb/docs-489-config-activation_deadline-new-parameter/

• Docs follow-up: not necessary / new issue

• [ ] Changelog is updated