Add config option for DB_USE_ENCRYPTION

[acelaya]

Part of shlinkio/shlink#2206

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.78%. Comparing base (9a7d414) to head (eb5450a).
Report is 3 commits behind head on develop.

Additional details and impacted files

@@              Coverage Diff              @@
##             develop     #233      +/-   ##
=============================================
+ Coverage      97.76%   97.78%   +0.01%     
- Complexity       326      328       +2     
=============================================
  Files             98       99       +1     
  Lines            940      948       +8     
=============================================
+ Hits             919      927       +8     
  Misses            21       21              

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