Include more details in InitializeCorrespondence response

[CelineTrammi]

Description

Changed InitializeCorrespondence and its response body to include more information about the correspondence created.

• Status is included
• Recipient is included
• Notification details is included

The notification details contains a field for status. This tells us whether the notification order was a success, contact information was missing, or if the creation of the order failed.

This also caused many small changes to the tests, since retrieval of correspondenceId is done differently now.

Related Issue(s)

• Endre respons datastruktur for initialisering av melding #349

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)

[Ceredron]

Looks great!
However, as this is a breaking API change we should announce it in https://altinn.slack.com/archives/C068VA4SXFD
(All our consumers are still developing so should be alright).

We also need to update our OpenApi spec in altinn-studio-docs and the Postman collection in this repository.