When uploading multiple files for a media with source cardinality > 1 it creates many media

Problem/Motivation

With a gallery as an example, it would be a media that has image source but with cardinality > 1.
At the moment when you create such media using dropzonejs in the media library, by dragging 10 files in, it will create 10 media instead of 1 media referencing the 10 files.

Steps to reproduce

1. Setup media with image source but cardinality on field unlimited
2. Setup content type with reference to media and use media library
3. Create new content of this type and hit Add Media and then drag in 10 files
4. On next step you are now populating the data for 10 media, not 1 media with 10 files

Proposed resolution

Allow a global option to opt-in to combining multiple file uploads into 1 media by detecting the cardinality of the source and overriding processInputValues to generate 1 media instead of many.

Remaining tasks

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User interface changes

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API changes

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Data model changes

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