POST v1/Files/FileUpload

This endpoint uploads a file together with a few text fields, so the request body must be sent as
multipart/form-data (the same encoding a browser uses for a file-upload form). Do NOT send JSON.

In an API client (e.g. Postman): select the Body tab, choose "form-data", then add one row per
field below. Set each row's type to "Text" or "File" as shown in the Type column. For the "file"
row, switch the type to File and pick the file to upload; the client fills in the rest.

Fields:

Key        | Type | Example Value | Required | Description
-----------|------|---------------|----------|-------------------------------------------------
ContactID  | Text | 12345         | Yes      | ID of the contact to associate the uploaded file with.
FileName   | Text | example.pdf   | Yes      | Name to store the uploaded file under.
PolicyID   | Text | 6789,6790     | No       | One or more policy IDs to associate, comma-separated.
File       | File | example.pdf   | Yes      | The file to upload. Exactly one file part is allowed.

Notes:
- ContactID must be a whole number; PolicyID accepts a single ID (6789) or several (6789,6790).
- Send exactly one "file" part - multiple files in one request are rejected.
- On success the response returns the stored file's details (see Response Information below).

{
  "IsSuccess": true,
  "ErrorCode": "sample string 2",
  "ErrorMessage": "sample string 3",
  "InfoMessage": "sample string 4"
}

<ActionResultDTO xmlns:i="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://schemas.datacontract.org/2004/07/QQSolutions.NextGen.ModelLibrary.DataTransferObjects">
  <ErrorCode>sample string 2</ErrorCode>
  <ErrorMessage>sample string 3</ErrorMessage>
  <InfoMessage>sample string 4</InfoMessage>
  <IsSuccess>true</IsSuccess>
</ActionResultDTO>