Implement `upgrade-relation` for control plane nodes #959

Job	Run time
unit-tests / Draft publish docs	18s
unit-tests / Inclusive naming	8s
unit-tests / Dockerfile lint	2s
unit-tests / Check libraries	3s
unit-tests / Check license headers	28s
unit-tests / Lint and unit tests	1m 30s
unit-tests / Lint metadata.yaml	4s
unit-tests / Shell scripts lint	2s
unit-tests / Style checker	12s
unit-tests / Required Test Status Checks	1s
	2m 48s

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