feat: add sqllite as an option to store signing keys

[1xstj]

Summary of changes
Changes introduced in this pull request:

Reference issue to close (if applicable)
Closes #684 #716

[codecov-commenter]

Codecov Report

Attention: 10 lines in your changes are missing coverage. Please review.

Comparison is base (d5512ea) 18.79% compared to head (7bb9c2d) 18.77%.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #723      +/-   ##
==========================================
- Coverage   18.79%   18.77%   -0.01%     
==========================================
  Files          80       80              
  Lines        5958     5963       +5     
==========================================
  Hits         1119     1119              
- Misses       4839     4844       +5     

Files	Coverage Δ
dkg-primitives/src/types.rs	0.00% <0.00%> (ø)
dkg-gadget/src/lib.rs	0.00% <0.00%> (ø)

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