Improve package size calculation on package details page

Context

We currently request the 100 most recent package files.

The total size of the package displayed on package detail page is calculated on the frontend by adding the size value of each package file.

Problem

This query will be modified to request either 10/20 package files per page when implementing Only the first 100 files are shown when browsin... (#353820 - closed), so the calculation of the package size will end up being incorrect.

Solution

The package size could be calculated on the backend & returned in the PackageDetailType GraphQL type.