PTII-145 Feature circuit breaker

[c4pone]

What does this PR do?

This will enable circuit breakers for each proxy

[codecov[bot]]

Codecov Report

Merging #269 into master will increase coverage by 0.4%. The diff coverage is 66.03%.

@@            Coverage Diff            @@
##           master     #269     +/-   ##
=========================================
+ Coverage   45.32%   45.72%   +0.4%     
=========================================
  Files          68       67      -1     
  Lines        2533     2539      +6     
=========================================
+ Hits         1148     1161     +13     
+ Misses       1325     1322      -3     
+ Partials       60       56      -4

Impacted Files	Coverage Δ
pkg/api/api.go	85.71% <ø> (ø)	:arrow_up:
pkg/proxy/register.go	0% <0%> (ø)	:arrow_up:
pkg/proxy/definition.go	64.7% <0%> (ø)	:arrow_up:
pkg/proxy/transport.go	0% <0%> (ø)	:arrow_up:
pkg/loader/loader.go	57.14% <100%> (+17.14%)	:arrow_up:
pkg/loader/api_loader.go	88.33% <100%> (+3.55%)	:arrow_up:
pkg/config/specification.go	57.37% <58.33%> (+0.23%)	:arrow_up:
pkg/plugin/oauth2/manager_factory.go	0% <0%> (ø)	:arrow_up:
pkg/plugin/oauth2/oauth.go	79.48% <0%> (ø)	:arrow_up:
... and 5 more

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[rafaeljesus]

We need to rethink this implementation, the failing target url should be remove from the balancer when CB trips and added back when it closes, otherwise we might have healthy target services but the failed one can trip the CB. Consul manages this out of the box, but if you don't operate janus in such way the CB won't be accurate

[italolelis]

@rafaeljesus can you take this task with @c4pone? It would be nice to have this feature as soon as possible, with the scenario that you just mentioned

[c4pone]

@italolelis I will close this pr for now and will think about a better solution next week together with @rafaeljesus. We will have a look into how we can trip the circuit breaker for each individual target without tripping for the whole endpoint. Also we were thinking about using a different circuit breaker library as hystrix-go is not the way to go.