Cherry-pick #17906 to 7.x: [Metricbeat GCP] Improve integration test to generate more specific data-*.json

[kaiyan-sheng]

Cherry-pick of PR #17906 to 7.x branch. Original message:

What does this PR do?

This PR is to improve TestData in integration test for each metricset under googlecloud module to generate more than one data.json file.

Why is it important?

This improves visibility on what events look like for different metric types. For example, in compute metricset, you can see different events like data_cpu.json, data_disk.json, data_firewall.json and data_network.json. Every time, code changes are made in stackdriver metricset, these data_*.json files should be regenerated to make sure they still look correct as expected.

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-platforms (Team:Platforms)