Adjust "Api::createRemoteLink" params with Jira API params

[aik099]

The following problems with the Api::createRemoteLink method are addressed:

• don't specify the globalId and relationship parameters with NULL values to the Jira REST API call, because it's not a guaranteed behavior of Atlassian to ignore NULL values
• made an $object method argument mandatory to be in line with an API specs
• added test

Closes #120

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 64.52%. Comparing base (236316d) to head (6c93c57).
Report is 2 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #231      +/-   ##
============================================
+ Coverage     63.17%   64.52%   +1.35%     
+ Complexity      208      207       -1     
============================================
  Files            10       10              
  Lines           687      685       -2     
============================================
+ Hits            434      442       +8     
+ Misses          253      243      -10     

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