Cherry-pick #19433 to 7.x: [MetricBeat] set tags correctly if the dimension value is ARN

[kaiyan-sheng]

Cherry-pick of PR #19433 to 7.x branch. Original message:

What does this PR do?

This PR is to fix setting resource tags when dimension value is ARN format, I found this issue in AWS/DDoSProtection namespace metrics.

Why is it important?

cloudwatch module should set event tags correctly if dimension value is ARN format and tags.resource_type_filter param is configured

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 [MetricBeat]set resource tags if dimension value is ARN #19111

Screenshots

test with aws shield service and EIP resource , I have put some demo metrics before running test ,so the namespace is DDoSProtection. The actual value is AWS/DDoSProtection if you get metrics that created by aws.

metricbeat.modules:
  - module: aws
    period: 1h
    access_key_id: 
    secret_access_key: 
    metrics:
      - namespace: DDoSProtection
        statistic: ['Maximum']
        name:
          [
            'DDoSDetected',
            'DDoSAttackBitsPerSecond',
            'DDoSAttackPacketsPerSecond',
            'DDoSAttackRequestsPerSecond',
          ]
        tags.resource_type_filter: ec2:elastic-ip

[elasticmachine]

Pinging @elastic/integrations-platforms (Team:Platforms)

[elasticmachine]

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• Build Cause: [Branch indexing]

• Start Time: 2020-07-02T09:26:24.395+0000

• Duration: 71 min 52 sec

Test stats 🧪

Test	Results
Failed	0
Passed	539
Skipped	128
Total	667