refactor go plugin

[debugtalk]

• feat: add github.com/httprunner/hrp/plugin sub-module
• feat: add scaffold for plugin
• feat: catch Interrupt and SIGTERM signals to ensure plugin quitted
• change: report event for initializing plugin
• doc: add plugin docs
• refactor: plugin structure

[codecov-commenter]

Codecov Report

Merging #59 (938a01e) into main (486d549) will increase coverage by 1.11%.
The diff coverage is 69.56%.

@@            Coverage Diff             @@
##             main      #59      +/-   ##
==========================================
+ Coverage   55.99%   57.10%   +1.11%     
==========================================
  Files          31       28       -3     
  Lines        3479     3292     -187     
==========================================
- Hits         1948     1880      -68     
+ Misses       1391     1283     -108     
+ Partials      140      129      -11     

Flag	Coverage Δ
unittests	57.10% <69.56%> (+1.11%)	⬆️

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Impacted Files	Coverage Δ
internal/scaffold/main.go	0.00% <0.00%> (ø)
internal/boomer/stats.go	92.59% <75.00%> (ø)
runner.go	68.55% <75.00%> (+1.56%)	⬆️
boomer.go	82.64% <80.76%> (+3.26%)	⬆️
parser.go	85.11% <100.00%> (+0.41%)	⬆️
plugin/common/call.go
plugin/common/init.go
plugin/shared/interface.go

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