Send datadog metrics in double instead of long

[lojzatran]

Fixes: https://commercetools.atlassian.net/browse/DEVX-460

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 14 lines in your changes missing coverage. Please review.

Project coverage is 9.75%. Comparing base (dddb9bb) to head (feb46fb).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
.../monitoring/datadog/DatadogResponseSerializer.java	0.00%	7 Missing ⚠️
...commercetools/monitoring/datadog/DatadogUtils.java	0.00%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              main    #727      +/-   ##
==========================================
- Coverage     9.75%   9.75%   -0.01%     
  Complexity    1873    1873              
==========================================
  Files         6796    6796              
  Lines        66318   66319       +1     
  Branches       268     268              
==========================================
  Hits          6469    6469              
- Misses       59684   59685       +1     
  Partials       165     165              

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