Add endpoint for IoT billing usage

[api-clients-generation-pipeline]

See DataDog/datadog-api-spec#784

[codecov-io]

Codecov Report

Merging #184 (b6bfa8d) into master (51a9944) will decrease coverage by 0.23%.
The diff coverage is 28.69%.

@@            Coverage Diff             @@
##           master     #184      +/-   ##
==========================================
- Coverage   39.05%   38.81%   -0.24%     
==========================================
  Files         796      798       +2     
  Lines       68274    69672    +1398     
==========================================
+ Hits        26667    27046     +379     
- Misses      41607    42626    +1019     

Impacted Files	Coverage Δ
...ib/datadog_api_client/v1/api/usage_metering_api.rb	7.76% <7.14%> (-0.03%)	⬇️
...atadog_api_client/v1/models/usage_io_t_response.rb	27.17% <27.17%> (ø)
...ib/datadog_api_client/v1/models/usage_io_t_hour.rb	28.72% <28.72%> (ø)
...datadog_api_client/v1/models/usage_summary_date.rb	47.64% <57.14%> (+0.10%)	⬆️
...dog_api_client/v1/models/usage_summary_date_org.rb	48.18% <57.14%> (+0.07%)	⬆️
...dog_api_client/v1/models/usage_summary_response.rb	49.76% <57.14%> (+<0.01%)	⬆️
lib/datadog_api_client/v1.rb	99.41% <100.00%> (+<0.01%)	⬆️
...2/models/application_key_response_included_item.rb	57.14% <0.00%> (-1.40%)	⬇️
...g_api_client/v2/models/application_key_response.rb	45.26% <0.00%> (-0.98%)	⬇️
...b/datadog_api_client/v2/models/api_key_response.rb	44.21% <0.00%> (-0.96%)	⬇️
... and 587 more

---

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[jirikuncar]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[codecov-commenter]

Codecov Report

❌ Patch coverage is 28.69198% with 169 lines in your changes missing coverage. Please review.
✅ Project coverage is 38.81%. Comparing base (51a9944) to head (b6bfa8d).
⚠️ Report is 2042 commits behind head on master.

Files with missing lines	Patch %	Lines
...ib/datadog_api_client/v1/models/usage_io_t_hour.rb	28.72%	67 Missing ⚠️
...atadog_api_client/v1/models/usage_io_t_response.rb	27.17%	67 Missing ⚠️
...ib/datadog_api_client/v1/api/usage_metering_api.rb	7.14%	26 Missing ⚠️
...datadog_api_client/v1/models/usage_summary_date.rb	57.14%	3 Missing ⚠️
...dog_api_client/v1/models/usage_summary_date_org.rb	57.14%	3 Missing ⚠️
...dog_api_client/v1/models/usage_summary_response.rb	57.14%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #184      +/-   ##
==========================================
- Coverage   39.05%   38.81%   -0.24%     
==========================================
  Files         796      798       +2     
  Lines       68274    69672    +1398     
==========================================
+ Hits        26667    27046     +379     
- Misses      41607    42626    +1019     

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