[AWS CloudWatch Metrics] Record previous endTime to use for next collection period

[kaiyan-sheng]

Proposed commit message

This PR is to record the previous endTime from the previous collection period to use for calculating the next collection start time and end time.
With using the previous endTime as the new startTime, we will not skip time range in collection.

This PR also changes log.logger from cloudwatch to aws.cloudwatch to match the other logger.

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.

Disruptive User Impact

N/A. User will see no gap in collection startTime and endTime, should be an enhancement.

How to test this PR locally

1. Pull this PR and run mage build to build Metricbeat locally.
2. ./metricbeat modules enable aws
3. Configure in aws.yml:

- module: aws
  period: 5m
  metricsets:
    - cloudwatch
  include_linked_accounts: true
  metrics:
    - namespace: AWS/RDS

4. Run metricbeat with debug log on
5. Check metricbeat log to make sure startTime and endTime are connected for all collection periods.

[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @kaiyan-sheng? 🙏.
For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change)

To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-8./d is the label to automatically backport to the 8./d branch. /d is the digit

[mergify]

backport-8.x has been added to help with the transition to the new branch 8.x.
If you don't need it please use backport-skip label and remove the backport-8.x label.

[elasticmachine]

Pinging @elastic/obs-ds-hosted-services (Team:obs-ds-hosted-services)

[Kavindu-Dodan]

LGTM