Improve sorting of initiative members

[petertrr]

What's done:

• Extract sorting logic into an interface
• Sort by base modifier if initiatives are equal

[codecov]

Codecov Report

Merging #3 (1a79547) into main (3177b5c) will decrease coverage by 0.31%.
The diff coverage is 81.81%.

@@             Coverage Diff              @@
##               main       #3      +/-   ##
============================================
- Coverage     83.78%   83.47%   -0.32%     
- Complexity       31       34       +3     
============================================
  Files             4        5       +1     
  Lines           111      121      +10     
  Branches         17       19       +2     
============================================
+ Hits             93      101       +8     
- Misses            9       10       +1     
- Partials          9       10       +1     

Flag	Coverage Δ
unittests	83.47% <81.81%> (-0.32%)	⬇️

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Impacted Files	Coverage Δ
...ithub/petertrr/initbot/sorting/DescendantSorter.kt	77.77% <77.77%> (ø)
...in/kotlin/io/github/petertrr/initbot/Initiative.kt	78.87% <100.00%> (+0.30%)	⬆️

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