feat: file upload as request body

[Tanish2002]

PR Description

• Enables direct file uploads using the application/octet-stream content type. The file's binary data is transmitted as the raw request body.

• Introduces the requestFile state variable within the request model. This ensures clean separation between file uploads and other request body types (i.e, text or JSON), preventing conflicts when switching input formats.

Please tell me if I need to fix up all the codegens and their corresponding tests.

Some screenshots:

1. successful upload:
   
2. Failed upload due to large payload:
   

Related Issues

• Related Issue Support File as Request Body #352
• Closes Support File as Request Body #352

Checklist

• I have gone through the contributing guide
• I have updated my branch and synced it with project main branch before making this PR
• I have run the tests (flutter test) and all tests are passing.

Added/updated tests?

• No, and this is why: I need help with what tests I need to add, and need confirmation if the new state variable is accepted.