Allow request mappings to handle a request based on host

[jwgmeligmeyling]

Fixes #121

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 50.00000% with 5 lines in your changes missing coverage. Please review.

Project coverage is 90.58%. Comparing base (f6311c9) to head (7c4993c).
Report is 29 commits behind head on master.

Files with missing lines	Patch %	Lines
...ron/configuration/RequestMappingConfiguration.java	50.00%	2 Missing ⚠️
...charon/configuration/RequestMappingConfigurer.java	0.00%	2 Missing ⚠️
...ylec/charon/forwarding/RequestMappingResolver.java	75.00%	0 Missing and 1 partial ⚠️

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Additional details and impacted files

@@             Coverage Diff              @@
##             master     #123      +/-   ##
============================================
- Coverage     90.80%   90.58%   -0.23%     
- Complexity      542      544       +2     
============================================
  Files           167      167              
  Lines          1849     1858       +9     
  Branches         54       55       +1     
============================================
+ Hits           1679     1683       +4     
- Misses          148      152       +4     
- Partials         22       23       +1     

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[mkopylec]

Same thing must be done for webflux module

[mkopylec]

Unit tests for this feature must be added