Add multipart/form-data support

[tonyskansf]

This pull request adds multipart/form-data content type upload support on top of the existing functionality in #43. Also, the changes contain an example showcasing the usage of the API.

Implementation

MultipartFormDataEncoder

Provides two ways of encoding the MultipartFormData: either in-memory encoding or encoding to disk. In-memory encoding is suitable for small payloads while encoding to disk is preferred and more efficient for large payloads to prevent memory issues.

Regardless of the encoding type, all data are encoded into this representation:

--boundary-{some id}
Content-Disposition: form-data; name="field-name"

{Field data}
--boundary-{some id}
Content-Disposition: form-data; name="attachment"; filename="file.txt"
Content-Type: text/plain

{Contents of the file}
--boundary-{some id}--

Usage

let uploadManager = UploadAPIManager()

// Get form data from the user (multipart form body parts)
let textFieldData = Data(text.utf8)
let attachmentUrl = URL(string: "path/to/file")!

// Add them to the MultipartFormData instance
let multipartFormData = MultipartFormData(/* boundary: override boundary */)
multipartFormData.append(textFieldData, name: "text-field")
try multipartFormData.append(from: attachmentUrl, name: "attachment-field")

// Send request
try await uploadManager.upload(
  multipartFormData: multipartFormData,
  to: endpoint,
  retryConfiguration: .default
)

[brenovaladao]

🪙

[cejanen]

I left some comments in first round

[cejanen]

One thing left on my side... @tonyskansf
otherwise we're done here 👍