create coverage data in monorepo-friendly way

[matt-codecov]

needed for https://github.com/codecov/umbrella/pull/17

currently the docker image is built and coverage data is generated as if shared is its own repo and all the files are in the repo root. in umbrella that is no longer true - shared exists in libs/shared/ and we want that prefix to be applied to every source file we have data for

this PR sets up shared in /app/libs/shared instead of /app inside the docker container

• for PRs in shared, path fixing strips those extra directories off the path and nothing is different (see this PR's indirect changes for example - if paths were not the same we would see a bunch of "No data" entries)
• for PRs in umbrella, path fixing will strip /app but libs/shared will remain like we want (see https://github.com/codecov/umbrella/pull/17 for example)

[codspeed-hq]

CodSpeed Performance Report

Merging #532 will create unknown performance changes

_{Comparing pr532 (941a8ce) with main (fd58134)}

Summary

⚠️ No benchmarks were detected in both the base of the PR and the PR.\

[codecov-notifications]

Codecov Report

All modified and coverable lines are covered by tests ✅

✅ All tests successful. No failed tests found.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.51%. Comparing base (fd58134) to head (941a8ce).
Report is 1 commits behind head on main.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #532   +/-   ##
=======================================
  Coverage   88.51%   88.51%           
=======================================
  Files         451      451           
  Lines       13127    13127           
  Branches     1529     1529           
=======================================
  Hits        11620    11620           
  Misses       1184     1184           
  Partials      323      323           

Flag	Coverage Δ
shared-docker-uploader	88.51% <ø> (ø)

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