修复injector挂载sermant会跟skywalking产生冲突的问题

[provenceee]

【修复issue】 #1258

【修改内容】修改injector注入命令的行为

【用例描述】注入行为分别为before、after、ignore时，是否可以按预期注入命令

【自测情况】before时，在原命令前注入，after时，在原命令后注入，ignore时，不注入

【影响范围】需要更新文档

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (4d207cf) 41.44% compared to head (21367c5) 41.44%.
Report is 1 commits behind head on develop.

Additional details and impacted files

@@            Coverage Diff             @@
##             develop    #1261   +/-   ##
==========================================
  Coverage      41.44%   41.44%           
  Complexity      3212     3212           
==========================================
  Files            821      821           
  Lines          18066    18066           
  Branches        1963     1963           
==========================================
  Hits            7487     7487           
  Misses          9641     9641           
  Partials         938      938           

Flag	Coverage Δ
unittests	41.44% <ø> (ø)

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