Support for per-input transformers

[Anilm3]

Support per-input transformers with the schema of the following example:

"inputs": [
  {
    "address": "http.client_ip",
    "key_path": [],
    "transformers": []
  }
],

[codecov-commenter]

Codecov Report

Merging #170 (f8235da) into master (ce0dd1e) will increase coverage by 0.27%.
The diff coverage is 57.44%.

@@            Coverage Diff             @@
##           master     #170      +/-   ##
==========================================
+ Coverage   63.82%   64.09%   +0.27%     
==========================================
  Files          65       65              
  Lines        3267     3284      +17     
  Branches     1527     1533       +6     
==========================================
+ Hits         2085     2105      +20     
+ Misses        314      308       -6     
- Partials      868      871       +3     

Flag	Coverage Δ
waf_test	64.09% <57.44%> (+0.27%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/parser/parser_v1.cpp	24.50% <0.00%> (-0.25%)	⬇️
src/parser/parser_v2.cpp	41.94% <54.83%> (+1.56%)	⬆️
src/condition.cpp	55.00% <60.00%> (+1.66%)	⬆️
src/PWTransformer.cpp	80.95% <100.00%> (+1.09%)	⬆️
src/condition.hpp	100.00% <100.00%> (ø)

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