Package details page: add loader for Other versions tab

Context

when you land on the package details page, for other versions, we just need the count. We could thus delay loading the version details at a later point. Ideally, that later point could be when the user clicks on other versions, this way, if other versions are not accessed, the versions details are not loaded.

Implementation guide

• Keep only version count in versions fragment on the package details GraphQL query.
• Extract the rest into a new GraphQL query to versions.
• Use the query within the package details page package_versions_list component
• Use existing loader to render loading content.
• Bonus: Make package_versions_list async component