Change non-standard return data format of ProjectIrodsFileListAPIView

[mikkonie]

The format of the return data is currently inexplicably an irods_data object with the actual list contained within. This goes against SODAR Core and SODAR conventions and also would make it confusing once we implement pagination (see #1996).

This is technically a breaking change, but as we can make breaking changes before introducing new versioning in v1.0, it can be done.

Existing clients need to be updated to expect a pure list.

Tasks

• Update return data in view
• Update tests
• Update docstring with full description of return data
• Update docs (including release notes for breaking API change)

[mikkonie]

Done.