[PS-1252] Fix Content Type for file upload

[manofthepeace]

Type of change

• [x] Bug fix
• [ ] New feature development
• [ ] Tech debt (refactoring, code cleanup, dependency upgrades, etc)
• [ ] Build/deploy pipeline (DevOps)
• [ ] Other

Objective

Fixes https://github.com/bitwarden/mobile/issues/2018

Code changes

• **BitwardenFileUploadService.cs ** Sets the content-type of the data/file upload to application/octet-stream to be consistent with other bitwarden client.

Before you submit

• [x] I have checked for formatting errors (dotnet tool run dotnet-format --check) (required)
• [ ] I have added unit tests where it makes sense to do so (encouraged but not required)
• [ ] This change requires a documentation update (notify the documentation team)
• [ ] This change has particular deployment requirements (notify the DevOps team)

[CLAassistant]

All committers have signed the CLA.

[bitwarden-bot]

Thank you for your contribution! We've added this to our internal Community PR board for review. ID: PS-1252

[aj-rosado]

Thank you for your contribution, I'm merging this change. It will be part of an upcoming release!