blob/fileblob: Allow customization of the FileMode

[vangent]

Fixes #3423

[codecov]

Codecov Report

Attention: Patch coverage is 90.00000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 73.15%. Comparing base (be1b4ae) to head (bb53595).
Report is 1 commits behind head on master.

Files	Patch %	Lines
blob/fileblob/fileblob.go	90.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3426      +/-   ##
==========================================
+ Coverage   73.12%   73.15%   +0.02%     
==========================================
  Files         113      113              
  Lines       14864    14872       +8     
==========================================
+ Hits        10870    10880      +10     
+ Misses       3219     3218       -1     
+ Partials      775      774       -1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.