feat: add DefaultPlugin

[soulbird]

Add DefaultPlugin so that we don't need to reimplement all the methods.

[codecov-commenter]

Codecov Report

Merging #92 (a8ec02b) into master (d283ba2) will decrease coverage by 1.97%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #92      +/-   ##
==========================================
- Coverage   82.01%   80.04%   -1.98%     
==========================================
  Files          14       14              
  Lines         901      897       -4     
==========================================
- Hits          739      718      -21     
- Misses        117      133      +16     
- Partials       45       46       +1     

Impacted Files	Coverage Δ
cmd/go-runner/plugins/fault_injection.go	61.29% <ø> (+1.91%)	⬆️
cmd/go-runner/plugins/limit_req.go	81.81% <ø> (+3.55%)	⬆️
cmd/go-runner/plugins/response_rewrite.go	82.60% <ø> (+3.44%)	⬆️
cmd/go-runner/plugins/say.go	77.77% <ø> (+4.09%)	⬆️
internal/server/server.go	49.20% <0.00%> (-16.67%)	⬇️

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