Add code to validate the request body when mocking requests

[MordFustang21]

No description provided.

[codecov]

Codecov Report

Merging #45 into master will increase coverage by 0.58%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master      #45      +/-   ##
==========================================
+ Coverage   42.27%   42.85%   +0.58%     
==========================================
  Files          10       10              
  Lines         660      672      +12     
==========================================
+ Hits          279      288       +9     
+ Misses        345      343       -2     
- Partials       36       41       +5

Impacted Files	Coverage Δ
request.go	18.02% <33.33%> (+0.83%)	⬆️
fetchermock/client.go	50% <0%> (+5.68%)	⬆️

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