Cherry-pick #19660 to 7.x: [MetricBeat] support wildcard * dimension value in AWS CloudWatch module

[kaiyan-sheng]

Cherry-pick of PR #19660 to 7.x branch. Original message:

• Enhancement

What does this PR do?

• support wildcard * dimension value in AWS CloudWatch metrics config
• update document with example config

Why is it important?

Now we must set explicit dimension value to filter out CloudWatch metrics. It will be flexible if we can support wildcard * in value param.

current config example:

- module: aws
  period: 300s
  metricsets:
    - cloudwatch
  metrics:
    - namespace: AWS/ApplicationELB
      statistic: ['Maximum']
      name: ['UnHealthyHostCount']
      dimensions:
        - name: LoadBalancer
          value: "lb id"
        - name: TargetGroup
          value: "tg id"

with the enhancement:

- module: aws
  period: 300s
  metricsets:
    - cloudwatch
  metrics:
    - namespace: AWS/ApplicationELB
      statistic: ['Maximum']
      name: ['UnHealthyHostCount']
      dimensions:
        - name: LoadBalancer
          value: "*"
        - name: TargetGroup
          value: "*"

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] AWS module support wildcard format dimension value to reduce the metrics count  #18050

[elasticmachine]

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

[elasticmachine]

💚 Build Succeeded

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Build stats

• Build Cause: [Pull request #19714 updated]

• Start Time: 2020-07-08T16:11:41.628+0000

• Duration: 42 min 37 sec

Test stats 🧪

Test	Results
Failed	0
Passed	729
Skipped	72
Total	801

[kaiyan-sheng]

jenkins, run the tests please