Trigger a background worker to generate npm metadata

🌱 Context

In order to keep a metadata up to date we need to regenerate it when events that change included data happen.

⚒ Proposal

Trigger a background worker to generate or regenerate npm metadata when:

1. A package is created or deleted.
2. A package file is deleted.
3. A tag is created, deleted or updated.
4. Packages metadata endpoint is hit but metadata cache is missing.

Important

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