WIP: Add support for extra_headers in upload request

[victorli-cloudinary]

Brief Summary of Changes

Add support for extra_headers in upload reqest

What Does This PR Address?

• [ ] GitHub issue (Add reference - #XX)
• [ ] Refactoring
• [X] New feature
• [ ] Bug fix
• [X] Adds more tests

Are Tests Included?

• [X] Yes
• [ ] No

[cloudinary-pkoniu]

@victorli-cloudinary Can you open this PR again as a draft PR? I'd like to avoid unnecessary merge.