Add support for the confirm complete feature

[SandGrainOne]

Description

Altinn CLI needs to have a feature that can help an Application Owner confirm that they have completed the processing of an instance. The action would allow Altinn to delete the data and the instance if the instance owner wants it removed. Not performing the action would force Altinn to keep the data stored indefinitely.

Acceptance criteria

• Using the new "confirm complete" command for an instance adds the org name of the caller to the CompleteConfirmations list on the instance.

Specification tasks

• Identify the best command structure for the new command. New command or subcommand on storage.
• Define development tasks.

Development tasks

Add tasks here

Definition of done

Verify that this issue meets DoD (Only for project members) before closing.

• Documentation is updated (if relevant)
  • Technical documentation (docs.altinn.studio)
  • User documentation (altinn.github.io/docs)
• QA
• Manual test is complete (if relevant)
• Automated test is implemented (if relevant)
• All tasks in this userstory are closed (i.e. remaining tasks are moved to other user stories or marked obsolete)