[Metricbeat] Add stackdriver metricset for googlecloud module

[kaiyan-sheng]

Similar to cloudwatch in aws module, we should create a stackdriver metricset for googlecloud module.

Modules

For a metricset to go GA, the following criterias should be met:

• Supported versions are documented
• Supported operating systems are documented (if applicable)
• Integration tests exist
• System tests exist
• Automated checks that all fields are documented
• Documentation
• Fields follow ECS and naming conventions
• Dashboards exists (if applicable)
• Kibana Home Tutorial (if applicable)
  • Open PR against Kibana repo with tutorial. Examples can be found here.

Metricbeat module

• Example data.json exists and an automated way to generate it exists (go test -data)
• Test environment in Docker exist for integration tests

[andresrc]

@kaiyan-sheng can you link the relevant PRs and update the status? Thanks!

[kaiyan-sheng]

Here is the PR for adding aligner parameter and documentation into stackdriver: #17719