Move Delivery Retry logic outside EmbraceApiService.

[lucaslabari]

Goal

• Moved logic related to retry failed network calls from EmbraceApiService to a new class EmbraceDeliveryRetryManager.
• Moved related unit tests too.

Testing

• Updated existing unit tests.

[codecov]

Codecov Report

Merging #49 (4dae99c) into master (143544f) will decrease coverage by 0.30%.
Report is 7 commits behind head on master.
The diff coverage is 70.93%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #49      +/-   ##
==========================================
- Coverage   73.76%   73.47%   -0.30%     
==========================================
  Files         305      306       +1     
  Lines       10053    10070      +17     
  Branches     1447     1448       +1     
==========================================
- Hits         7416     7399      -17     
- Misses       2067     2103      +36     
+ Partials      570      568       -2     

Files	Coverage Δ
...oid/embracesdk/injection/EssentialServiceModule.kt	95.58% <100.00%> (+0.20%)	⬆️
.../android/embracesdk/comms/api/EmbraceApiService.kt	19.07% <14.28%> (-28.37%)	⬇️
...esdk/comms/delivery/EmbraceDeliveryRetryManager.kt	73.97% <73.97%> (ø)

... and 3 files with indirect coverage changes