Add staging.jars.allowedenvdirs setting

[kellen]

Adds staging.jars.allowedenvdirs which lets users whitelist specific env dirs for jar-staging purposes, e.g. if a user wants to stage jars from ~/.cache/bazel_dir

[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 61.97%. Comparing base (dbf5b5c) to head (b40560a).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
.../src/main/scala/com/spotify/scio/ScioContext.scala	83.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5958      +/-   ##
==========================================
+ Coverage   61.95%   61.97%   +0.02%     
==========================================
  Files         323      323              
  Lines       11727    11731       +4     
  Branches      821      834      +13     
==========================================
+ Hits         7265     7270       +5     
+ Misses       4462     4461       -1     

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