Add support for detailed file status

[Ceredron]

Description

The consumer should know why an upload has failed. We retain the FileStatus enum field to make it easy to add logic to the consumer response handler.

Related Issue(s)

• Legg til utfyllende statustekst #272

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)