output/cloudv2: Fix insights client initialization

[Blinkuu]

Fixes a bug where K6_CLOUD_TRACES_HOST didn't work with default values.

[codecov-commenter]

Codecov Report

Merging #3184 (28a9ee9) into master (c66c1be) will increase coverage by 0.01%.
The diff coverage is 0.00%.

❗ Current head 28a9ee9 differs from pull request most recent head e137df8. Consider uploading reports for the commit e137df8 to get more accurate results

@@            Coverage Diff             @@
##           master    #3184      +/-   ##
==========================================
+ Coverage   72.80%   72.81%   +0.01%     
==========================================
  Files         256      256              
  Lines       19697    19697              
==========================================
+ Hits        14340    14342       +2     
+ Misses       4462     4460       -2     
  Partials      895      895              

Flag	Coverage Δ
ubuntu	72.75% <0.00%> (+0.02%)	⬆️
windows	72.63% <0.00%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
output/cloud/expv2/output.go	64.77% <0.00%> (ø)

... and 1 file with indirect coverage changes