Fixes #1957: Ensure unique S3 object keys by adding numeric suffix.

[abhinavxd]

• Removed unused functions and variables in filesystem.go

[knadh]

Thanks for the PR!

Thinking about it, rather than each provider implementing its own logic, it'd be simpler to do it centrally in handleUploadMedia() and check in the database. Roughly:

• Add a GetMediaByFilename(fname, provider string) function to core/media.go
• This will require a new query to be added to queries.sql also
• Use this in handleUploadMedia() to assert the incoming filename and tweak it if it already exists.
• Remove the existing assertion logic from the filesystem provider.

[abhinavxd]

Yep, makes sense. I will update the PR.

[abhinavxd]

I added the DB level check for unique filename, but it fails when multiple files with the same name are selected for upload.

The previous provider level check handles this properly, Could not recreate it with provider level checks.

[abhinavxd]

@knadh Changes made as discussed.

[knadh]

Couple minor things to fix.

[abhinavxd]

Made the changes requested.