Add connection_class as input param

[botzill]

Added custom connection_class for the use cases when you want to configure custom connection, like custom proxies or other params.

[codecov]

Codecov Report

Merging #1 (1c38699) into master (a7993c1) will increase coverage by 0.23%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master       #1      +/-   ##
==========================================
+ Coverage   81.35%   81.58%   +0.23%     
==========================================
  Files           2        2              
  Lines         236      239       +3     
  Branches       42       42              
==========================================
+ Hits          192      195       +3     
  Misses         24       24              
  Partials       20       20              

Impacted Files	Coverage Δ
elasticecslogging/handlers.py	81.03% <100.00%> (+0.24%)	⬆️

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[tommycahir]

@botzill It should probably be noted that 'RequestsHttpConnection' was removed from 'elasticsearch' and is replaced with RequestsHttpNode from elastic_transport elastic/elasticsearch-py#1778 (comment) so you may need to set the default to RequestsHttpNode and hope it gets merged..