fix: use strategic merge patch to merge built-in and user provided config

[alexmt]

Closes #69

[codecov]

Codecov Report

Merging #74 into master will decrease coverage by 1.13%.
The diff coverage is 58.33%.

@@            Coverage Diff             @@
##           master      #74      +/-   ##
==========================================
- Coverage   56.59%   55.45%   -1.14%     
==========================================
  Files          20       20              
  Lines        1009      990      -19     
==========================================
- Hits          571      549      -22     
- Misses        359      361       +2     
- Partials       79       80       +1     

Impacted Files	Coverage Δ
notifiers/notifiers.go	0.00% <ø> (ø)
cmd/controller.go	32.75% <33.33%> (-0.58%)	⬇️
shared/settings/settings.go	72.88% <61.90%> (-8.37%)	⬇️

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