[firebase_storage] putNetwork alt putStream for uploading bigger files on Web

[MrAlek]

Currently, the only stream-based API for uploading files is putFile, which only works with local files and thus not on the web platform because reasons.

All other APIs (putBlob, putData, putString) require to load the file contents in-memory first which is inefficient and impractical for bigger files such as videos which can be multiple gigabytes.

To have complete web support we need a new API which can handle reading remote file URLs. This could either be a specific putNetwork/ putURL, or (even better) a generic putStream which could easily work for local files, remote URLs and more complex situations such as piping live-recorded video straight to Firebase Storage.