feat: reverts message in json output and allows configuration

[fmartingr]

• Reverts back the responses of the API to be like {"ok": bool, "message": body}
• Allows using the future response by setting the X-Shiori-Request-Format to new

This will be the default until 2.0 is released with the removal of the legacy API.

[codecov]

Codecov Report

Attention: Patch coverage is 77.33333% with 17 lines in your changes missing coverage. Please review.

Project coverage is 50.08%. Comparing base (d419818) to head (d50a6bb).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
internal/http/middleware/message_response.go	75.80%	10 Missing and 5 partials ⚠️
internal/http/webcontext/context.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1082      +/-   ##
==========================================
+ Coverage   49.68%   50.08%   +0.40%     
==========================================
  Files          73       74       +1     
  Lines        7320     7389      +69     
==========================================
+ Hits         3637     3701      +64     
  Misses       3366     3366              
- Partials      317      322       +5     

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