WIP: Add composer packages feature

⚠️ Add comments to the new MR here: !22415 (closed)

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Due to a broken MR https://gitlab.com/gitlab-org/gitlab/merge_requests/9012 i was adviced to create this one

What does this MR do?

Upload Composer packages to packages page and add API endpoints

What are the relevant issue numbers?

See #15886 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• EE specific content should be in the top level /ee folder
• Security reports checked/validated by reviewer

Related Merge Requests

• Docs: !18054 (closed)
• GUI Changes: !9306 (closed)