Add /upload_sample route to allow upload new speakers using Web API

* Added route to upload sample into speakers folder, so you can upload new speakers using API * Added python-multipart to requirements <!-- This is an auto-generated comment: release notes by coderabbit.ai --> ## Summary by CodeRabbit - **New Features** - Introduced a new endpoint for uploading WAV files, which saves the file and returns the filename. - **Dependencies** - Added `python-multipart` package to support file uploads. <!-- end of auto-generated comment: release notes by coderabbit.ai -->