Persisted Sessions logging

[bitsandfoxes]

Currently persisted sessions not found log as an error for anything else but FileNotFoundException.
I added DirectoryNotFound so both now both log as debug, everything else as error.
Added additional tests for exception type.

[codecov-commenter]

Codecov Report

Merging #1125 (8b547be) into main (10b4f6b) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1125      +/-   ##
==========================================
+ Coverage   80.63%   80.65%   +0.02%     
==========================================
  Files         197      197              
  Lines        6589     6592       +3     
  Branches     1453     1455       +2     
==========================================
+ Hits         5313     5317       +4     
  Misses        802      802              
+ Partials      474      473       -1     

Impacted Files	Coverage Δ
src/Sentry/GlobalSessionManager.cs	71.20% <100.00%> (+0.73%)	⬆️

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