Feature/duplicate confirm handling

[Andreass2]

Description

Duplicate handling on confirm request.
It uses idempotency logic to avoid proccessing of events multiple times. In the processing of the request it also checks if the file is already marked as downloaded by the recipient.

The Idempotency can now easily be used for other processing functions by sending a unique string and a prossessing funtion

Also added a start script for starting local dev.

Related Issue(s)

• Brøytetesting av overgangsløsning #309

Verification

• Your code builds clean without any errors or warnings
• Manual testing done (required)
• Relevant automated test added (if you find this hard, leave it and we'll help out)
• All tests run green

Documentation

• User documentation is updated with a separate linked PR in altinn-studio-docs. (if applicable)