[ISSUE #621] Support consume message directly

[maixiaohai]

What is the purpose of the change

issue #621

Brief changelog

Add func ConsumeMessageDirectly
Add unit test

Verifying this change

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[codecov-io]

Codecov Report

Merging #622 (f91f448) into master (378f68a) will decrease coverage by 0.37%.
The diff coverage is 2.32%.

@@            Coverage Diff             @@
##           master     #622      +/-   ##
==========================================
- Coverage   24.45%   24.08%   -0.38%     
==========================================
  Files          48       48              
  Lines        5050     5136      +86     
==========================================
+ Hits         1235     1237       +2     
- Misses       3612     3695      +83     
- Partials      203      204       +1     

Impacted Files	Coverage Δ
consumer/push_consumer.go	10.82% <0.00%> (-0.57%)	⬇️
internal/client.go	0.00% <0.00%> (ø)
internal/request.go	1.88% <0.00%> (-0.22%)	⬇️
internal/model.go	43.67% <50.00%> (+0.30%)	⬆️

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