Add config option to disable SSL verification

[hulkur]

Based on #255 by danielsimkus

Adds a config option to disable SSL verification on server connection.

.env
ELASTICSEARCH_SSL_VERIFICATION=false

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.01%. Comparing base (94365ad) to head (caea6b9).

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #283      +/-   ##
============================================
+ Coverage     95.99%   96.01%   +0.02%     
- Complexity      194      195       +1     
============================================
  Files            36       36              
  Lines           624      628       +4     
============================================
+ Hits            599      603       +4     
  Misses           25       25              

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