Avoid using shared cache for internally stored files

[Swatinem]

It is a bit wasteful to look up our internally hosted Symbols on GCS, just to store them on GCS again in the form of the shared cache.
We can avoid doing this needless duplication of roundtrips and storage.

We could also avoid using the shared cache for objects and bundle indexes that are stored in Sentry, but here the benefits are less clear, as avoiding shared cache would mean going through the Python abstraction. Right now, we rather waste a bit of storage in favor of avoiding Python.

These tradeoffs could potentially change in the future with a more efficient filestore implementation though.

#skip-changelog

[codecov]

Codecov Report

Merging #1320 (dd8e839) into master (d8704ed) will increase coverage by 0.01%.
The diff coverage is 90.32%.

@@            Coverage Diff             @@
##           master    #1320      +/-   ##
==========================================
+ Coverage   75.68%   75.70%   +0.01%     
==========================================
  Files          94       94              
  Lines       14701    14727      +26     
==========================================
+ Hits        11127    11149      +22     
- Misses       3574     3578       +4