[AWS] Add a new "Data Granularity" parameter in Cloudwatch metricbeat module

[girodav]

Describe the enhancement:

Introduce a new parameter that customers can use to define the granularity of the datapoints returned by GetMetricData API calls. The parameter should be name "Data Granularity" and to be passed as "Period" for every MetricDataQuery https://docs.aws.amazon.com/AmazonCloudWatch/latest/APIReference/API_MetricDataQuery.html created

Describe a specific use case for the enhancement or feature:

With the introduction of this new parameter, customer can retrieve high-granular data, but less frequently, leading to cost savings on their AWS bills.

Full context behind this enhancement can be found on this issue elastic/integrations#2913

Scenarios to test before releasing this new feature:

• "Data Granularity" set lower than "Collection Period" -> Metricbeat should collect data every collection period, with the specified granularity
• "Data Granularity" set higher than "Collection Period" -> Metricbeat should return a configuration error and fail to start
• "Data Granularity" equal to "Collection Period" -> Metricbeat should work as it currently does, without the introduction of this feature
• "Data Granularity" not set -> same as above
• "Data Granularity" set lower than "Collection Period" -> Metricbeat should report multiple data points per collection period (make sure to check the number of data points is correct)
• "Data Granularity" equal to "Collection Period" or when "Data Granularity" not set -> Metricbeat should only report one set of data points per collection period
• Test billing metricset with the granularity parameter different than the metricbeat collection period, and check the event output.