Service client

[benblack86]

Service client with load balancer and retries built in! Includes tests and doc changes.

Overall I feel like this is moving in the correct direction, but I think it can be cleaned up in future PRs. My problem is that we are squishing different functionality into the client trait. I think what we currently call clients, should be renamed connections. A client would then contain one-to-many connections, which it can manage. You can conceive that if you want to skip the client and just talk to the connection, that should be possible. Anyways, that can wait for another day.

@aliyakamercan @jlbelmonte @amotamed @DanSimon

[codecov-io]

Codecov Report

Merging #639 into develop will decrease coverage by <.01%. The diff coverage is 84.15%.

@@             Coverage Diff             @@
##           develop     #639      +/-   ##
===========================================
- Coverage    84.75%   84.74%   -0.01%     
===========================================
  Files           99      100       +1     
  Lines         4440     4518      +78     
  Branches       407      403       -4     
===========================================
+ Hits          3763     3829      +66     
- Misses         677      689      +12

Impacted Files	Coverage Δ
...ssus/src/main/scala/colossus/core/Connection.scala	68.18% <ø> (ø)	:arrow_up:
...lossus/src/main/scala/colossus/service/Async.scala	50% <ø> (ø)	:arrow_up:
...sus/src/main/scala/colossus/core/RetryPolicy.scala	90.9% <ø> (ø)	:arrow_up:
...in/scala/colossus/service/AsyncServiceClient.scala	87.17% <0%> (-7.27%)	:arrow_down:
...c/main/scala/colossus/protocols/http/package.scala	30.76% <100%> (ø)	:arrow_up:
...ain/scala/colossus/protocols/http/HttpClient.scala	88.88% <100%> (-1.12%)	:arrow_down:
...src/main/scala/colossus/metrics/ConfigHelper.scala	92.59% <100%> (+0.92%)	:arrow_up:
...ain/scala/colossus/service/ServiceClientPool.scala	100% <100%> (ø)	:arrow_up:
...s/src/main/scala/colossus/service/ServiceDSL.scala	81.13% <55.55%> (-2.55%)	:arrow_down:
...rc/main/scala/colossus/service/ServiceClient.scala	92.51% <75%> (+0.79%)	:arrow_up:
... and 10 more

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[amotamed]

LGTM 👍