Fix inline file upload

[TarasZakus]

Current version of bref/local-api-gateway supports only 'Content-Type: multipart/form-data',
whereas inline body (e.g. image/jpeg) is not encoded properly and the uploaded file is corrupted.

For example, the following request works:

PUT https://api.test/upload/profile-image
Content-Type: multipart/form-data;boundary="BoundaryDelimiter"
Accept: application/json

--BoundaryDelimiter
Content-Disposition: form-data; name="file"; filename="test.jpeg"
Content-Type: image/jpeg

< /home/images/test.jpeg
--BoundaryDelimiter--

, but this request doesn't work:

PUT https://api.test/upload/profile-image
Content-Type: image/jpeg
Accept: application/json
Content-Disposition: inline; filename="test.jpeg"

< /home/images/test.jpeg

Change in this PR resolves the issue.