Support url parameters

[stefanoj3]

What does this PR do?

Adds supports for named parameters in the target url.

Example Given this configuration

Definition{
    ListenPath: "/api/recipes/{id:[\\da-f]{24}}",
    Upstreams: &Upstreams{
        Balancing: "roundrobin",
        Targets:   []*Target{{Target: "http://localhost:9089/recipes/{id}"}},
    },
    Methods:    []string{"ALL"},
    StripPath:  false,
    AppendPath: false,
}

If I call /api/recipes/5252b1b5301bbf46038b473f my call should be forwarded to http://localhost:9089/recipes/5252b1b5301bbf46038b473f

[olvlvl]

WANT! https://github.com/hellofresh/janus/issues/260

[codecov[bot]]

Codecov Report

Merging #262 into master will decrease coverage by 0.17%. The diff coverage is 28.57%.

@@            Coverage Diff             @@
##           master     #262      +/-   ##
==========================================
- Coverage   45.21%   45.04%   -0.18%     
==========================================
  Files          66       67       +1     
  Lines        2433     2460      +27     
==========================================
+ Hits         1100     1108       +8     
- Misses       1279     1298      +19     
  Partials       54       54

Impacted Files	Coverage Δ
pkg/proxy/register.go	0% <0%> (ø)	:arrow_up:
pkg/router/listen_path_parameter_name_extractor.go	100% <100%> (ø)

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[stefanoj3]

@rafaeljesus updated with the changes you requested

[stefanoj3]

Updated with the requested changes and with the help of @rafaeljesus I added also an automation test

[rafaeljesus]

@stefanoj3 we could add this new feature on the docs as well https://github.com/hellofresh/janus/docs/proxy/routing_capabilities.md a simple example is enough

[stefanoj3]

Doc updated

[rafaeljesus]

@stefanoj3 @olvlvl really appreciate your effort to push this feature, thank you

[olvlvl]

Thanks guys! I'm really glad about this feature!