RDL file import in API is broken in several ways

Trying to automate RDL file upload using Invoke-PowerBIRestMethod and the /groups/<group>/imports POST endpoint seems borderline impossible currently - there are several problems:

• No examples online - every example uses Invoke-RestMethod (none of which work)

• Content-Type header parsing is broken, for example "multipart/form-data; boundary=someboundary" (with or without quotes around the boundary) results in an error saying that the header value is invalid. Same header works in Invoke-RestMethod. This makes it impossible to send multipart data as the boundary can't be specified.

• Every single permutation of trying to do an RDL import returns 400 with no other information and the documentation/Swagger doc doesn't really help. e.g do we need to supply datasetDisplayName with RDL even though there is no seperable dataset?

Any example of importing an RDL would be useful - I haven't found any at all using Invoke-PowerBIRestMethod and haven't found any with other cmdlets that work.

Start with the Invoke-PowerBIRestMethod cmdlet and the /groups//imports POST endpoint described in the issue. Reproduce the multipart/form-data boundary error and the 400 response for an RDL import; done means identifying working import parameters and providing an example or resolving the reported request handling problems.