Cherry-pick #18172 to 7.x: [Metricbeat] Add dashboard for googlecloud storage metricset

[kaiyan-sheng]

Cherry-pick of PR #18172 to 7.x branch. Original message:

What does this PR do?

This PR is to add dashboard for googlecloud storage 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.

How to test this PR locally

1. Make sure your GCP account for testing has storage buckets
2. Enable googlecloud module: ./metricbeat modules enable googlecloud
3. Edit modules.d/googlecloud.yml to:

- module: googlecloud
  metricsets:
    - storage
  project_id: "your project id"
  credentials_file_path: "your JSON credentials file path"
  exclude_labels: false
  period: 5m

4. Start metricbeat: ./metricbeat -e
5. Wait for 5 minutes and you should see data points in GCP storage dashboard.

Screenshots

[elasticmachine]

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

[ycombinator]

Backport LGTM.

[elasticmachine]

💚 Build Succeeded

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Build stats

• Build Cause: [Pull request Cherry-pick #18172 to 7.x: [Metricbeat] Add dashboard for googlecloud storage metricset #18257 opened]

• Start Time: 2020-05-05T17:07:38.943+0000

• Duration: 130 min 3 sec (7803122)

• Commit: 56a12c7

Test stats 🧪

Test	Results
Failed	0
Passed	2323
Skipped	560
Total	2883