SNOW-1825790 Separate secure storage managers based on file and keyring

[sfc-gh-pfus]

Description

SNOW-1825790 Separate secure storage managers to make them easier to extend.

Checklist

• Created tests which fail without the change (if possible)
• Extended the README / documentation, if necessary

[codecov]

Codecov Report

Attention: Patch coverage is 62.76596% with 70 lines in your changes missing coverage. Please review.

Project coverage is 82.16%. Comparing base (e5ae90f) to head (0265874).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
secure_storage_manager.go	61.53%	70 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1295      +/-   ##
==========================================
- Coverage   82.30%   82.16%   -0.14%     
==========================================
  Files          55       55              
  Lines       13600    13636      +36     
==========================================
+ Hits        11193    11204      +11     
- Misses       2407     2432      +25     

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