Add latency config option for aws-cloudwatch input

[kaiyan-sheng]

What does this PR do?

This PR is to add latency config parameter into Filebeat aws-cloudwatch input, similar to what we did in cloudwatch metricbeat metricset.
Some AWS services send logs to CloudWatch with a latency to process larger than aws-cloudwatch input scan_frequency. In this case, we need to use the latency config to shift the collection start time and end time in order to collect the logs.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Related issues

• Closes Filebeat CloudWatch input misses events #28133

[mergify]

This pull request does not have a backport label. Could you fix it @kaiyan-sheng? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v./d./d./d is the label to automatically backport to the 7./d branch. /d is the digit

NOTE: backport-skip has been added to this pull request.

[elasticmachine]

Pinging @elastic/integrations (Team:Integrations)

[elasticmachine]

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• Start Time: 2021-10-18T21:31:19.350+0000

• Duration: 108 min 35 sec

• Commit: 34cfa08

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Test	Results
Failed	0
Passed	7753
Skipped	1201
Total	8954

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