Add worker to trigger CreateMetadataCacheService

What does this MR do and why?

Add worker to trigger CreateMetadataCacheService

Screenshots or screen recordings

No.

How to set up and validate locally

All steps need to be executed in rails console

1. Create a new npm package:

   def fixture_file_upload(*args, **kwargs)
     Rack::Test::UploadedFile.new(*args, **kwargs)
   end
   
   package = FactoryBot.create(:npm_package, project: Project.first)

2. Enable npm_metadata_cache feature flag

   Feature.enable(:npm_metadata_cache, Project.first)

3. Trigger background worker

   Packages::Npm::CreateMetadataCacheWorker.new.perform(package.project_id, package.name)

4. Inspect changes: seek for the metadata cache object created for the package

   Packages::Npm::MetadataCache.find_by(package_name: package.name)

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #393636 (closed)