Feature/251 get available files

[tomshag]

Creates the Legacy HasAvailableFiles and GetAvailableFiles service.

Description

Added new services:
GetAvailableFiles: functions mostly like the regular GetAvailableFiles, reportee is submitted in OnBehalfOfConsumer rather than in token.
HasAvailableFiles: will not function like the regular HasAvailableFiles. This call will not be made "on behalf of" a consumer, as it is never authenticated or authorized through Altinn. Instead, the call is made with a list of recipients that Altinn will then check for available files and return regardless of access rights. (The final Altinn 2 code only replies with 'true' or 'false'.)

Related Issue(s)

• Overgangsløsning A2: BrokerBridge.GetAvailableFiles + HasAvailableFiles #251

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)

I am a bit unsure where this would be updated in docs.