Allow pluggable uploaders in Companion

[mifi]

Problem

People might want to handle the uploaded data in different ways. Currently we support s3, s3-multipart, multipart and tus, but some people want to do different things like:

• upload to one bucket if the file has this name, but to different bucket if a different name
• Upload all files to multiple buckets How to use multiple S3 buckets #3214
• check some auth before uploading based on some metadata
• want to upload the files to s3 and also save to an FTP and write som stuff to an SQL database
• and so many other requests

Solution

We already allow people to implement custom Providers (people can implement their own download sources like Google Drive, Dropbox etc), so why not also support custom Upload Destinations?

I did some testing and I don't think it's very hard to implement. Just need to make an API that's quite flexible for future enhancements.

Alternatives

Keep on adding features, options and switches to our existing Uploaders.