Add aggregate api v2 spec

[api-clients-generation-pipeline]

See DataDog/datadog-api-spec#465

[jirikuncar]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[codecov]

Codecov Report

Merging #406 into master will decrease coverage by 1.41%.
The diff coverage is 1.36%.

Impacted Files	Coverage Δ	Complexity Δ
...in/java/com/datadog/api/v2/client/api/LogsApi.java	64.70% <0.00%> (-21.01%)	5.00 <0.00> (ø)
...tadog/api/v2/client/model/LogsAggregateBucket.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
.../api/v2/client/model/LogsAggregateBucketValue.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...ient/model/LogsAggregateBucketValueTimeseries.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...model/LogsAggregateBucketValueTimeseriesPoint.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...adog/api/v2/client/model/LogsAggregateRequest.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...pi/v2/client/model/LogsAggregateRequestPaging.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...dog/api/v2/client/model/LogsAggregateResponse.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...api/v2/client/model/LogsAggregateResponseData.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...i/v2/client/model/LogsAggregateResponseStatus.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
... and 39 more