[GCP] Add GCP GKE Metricset

[legoguy1000]

What does this PR do?

Adds GCP GKE metricset

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.
• If I'm introducing a new feature, I have modified the Kibana version constraint in my package's manifest.yml file to point to the latest Elastic stack release (e.g. ^7.13.0).

Author's Checklist

• [ ]

How to test this PR locally

Related issues

• Relates Migrate some Metricbeat modules to GCP package #490
• Requires [GCP] Add GCP Compute Metricset #2301

Screenshots

[elasticmachine]

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• Reason: The PR is not allowed to run in the CI yet

• Start Time: 2021-12-02T23:24:32.964+0000

• Duration: 2 min 24 sec

• Commit: f2ec4bb

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[endorama]

Has been reported some issues related to the GKE Overview dashboard. To fix them the dashboard has been update in elastic/beats#29913.
Those changes should be reported in this PR too.