Migrate ec2 metricset to use cloudwatch input as light weight module

[kaiyan-sheng]

What does this PR do?

This PR is to migrate ec2 metricset to use cloudwatch input as light weight module. Two main parts in this PR:

1. In the original ec2 metricset, we are also making EC2 DescribeInstances API call to get metadata for each EC2 instance. This is added as a part of cloudwatch metricset now.
   You can see under ec2 metricset, there is only a manifest.yml file which defines cloudwatch as the input.

2. We need to keep backwards compatibility with metric names so dashboard can still be used.
   You can see rename processor is used in manifest.yml file under ec2 metricset to make sure with this PR we are not introducing breaking changes. Also please check the updated data.json file in ec2 metricset to see the renaming is effective.

Why is it important?

With this change, we no longer need to maintain the common code in both ec2 metricset and cloudwatch metricset.

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.

[elasticmachine]

Pinging @elastic/integrations (Team:Integrations)

[elasticmachine]

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Build stats

• Build Cause: Pull request #25924 updated

• Start Time: 2021-05-31T14:22:32.378+0000

• Duration: 78 min 22 sec

• Commit: 43ec3f0

Test stats 🧪

Test	Results
Failed	0
Passed	2033
Skipped	192
Total	2225

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Test stats 🧪

Test	Results
Failed	0
Passed	2033
Skipped	192
Total	2225

[kaiyan-sheng]

CI failure is also reported in auditbeat. It doesn't look like it's related to this PR: #25956

[mergify]

This pull request is now in conflicts. Could you fix it? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b refactor_cloudwatch_input upstream/refactor_cloudwatch_input
git merge upstream/master
git push upstream refactor_cloudwatch_input

[mtojek]

/test

[ChrsMark]

Nice to see this cleanup! Left some suggestions/comments but overall I'm ok with the change. Let me know what you think!

[ChrsMark]

Thanks!