Reduce package index building query usage

[MythicManiac]

Reduce the amount of queries executed when building the new package index by prefetching related objects. In exchange, this increases the memory consumption.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (c2ef429) 92.51% compared to head (8f63ef3) 92.51%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #917 +/- ## ======================================= Coverage 92.51% 92.51% ======================================= Files 275 275 Lines 8131 8131 Branches 771 771 ======================================= Hits 7522 7522 Misses 504 504 Partials 105 105 ```

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