refactor: campaign subscriptions

[ArnelaL]

refactor: campaign subscriptions

• remove noop action on campaign resource that was used to trigger subscriptions when campaign target was updated
• add subscriptions by campaign to campaign targets
• update the frontend accordingly

What this PR does / why we need it:

Additional documentation e.g. usage docs, diagrams, reviewer notes, etc.:

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[OmarBrbutovic]

🚀

[lusergit]

🚀 /fast-forward