services: Split endpoint and credential into different pair

[Xuanwo]

No description provided.

[codecov]

Codecov Report

Merging #34 into master will decrease coverage by 0.11%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #34      +/-   ##
==========================================
- Coverage   77.94%   77.83%   -0.12%     
==========================================
  Files           9        9              
  Lines         975      961      -14     
==========================================
- Hits          760      748      -12     
+ Misses        139      138       -1     
+ Partials       76       75       -1

Impacted Files	Coverage Δ
services/posixfs/meta.go	78.37% <ø> (ø)	⬆️
services/qingstor/service.go	63.55% <100%> (ø)	⬆️
services/qingstor/meta.go	65.53% <100%> (-1.29%)	⬇️

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