Feature/cancel initial subscriptions

Add the cancel_subscription workflow that allows for taking a subscription from INITIAL to TERMINATED.

Since it's a termination workflow, we can't change this from showing up differently (they're forcefully all called "Terminate router" in this case). But only one is available to run, so I'd say this is acceptable.

Also, I added some subtile warnings to prevent accidentally running this.

assigned to @karel.vanklink

added 1 commit

• a3a9bfa9 - Add unit test for cancellation workflow

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requested review from @simone.spinelli

added 8 commits

• a3a9bfa9...78f86145 - 4 commits from branch develop
• b33edef5 - Add cancel_subscription workflow
• fefb0436 - Update documentation
• e4ed0451 - Add db migration and translation key
• a3c56763 - Add unit test for cancellation workflow

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added 1 commit

• c4a1af80 - Update migration down_revision

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enabled an automatic merge when the pipeline for c4a1af80 succeeds

merged