Cherry-pick #25368 to 7.x: [FileBeat] GCP module enhancement - Populate orchestrator.* fields for K8S logs

[ChrsMark]

Cherry-pick of PR #25368 to 7.x branch. Original message:

What does this PR do?

This PR add the ability to populate orchestrator.* fields for GCP K8S logs. The cluster_name field from the original message was not kept in the logs, this field is important to analyze security events. I also tried to populate other orchestrator.* fields with information available in other fields of the original message.

Why is it important?

The cluster_name field from the original message was not kept in the logs, this field is important to analyze security events.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas

[elasticmachine]

Pinging @elastic/security-external-integrations (Team:Security-External Integrations)

[elasticmachine]

Pinging @elastic/integrations (Team:Integrations)

[elasticmachine]

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Build stats

• Build Cause: Pull request #26111 updated

• Start Time: 2021-06-02T10:17:30.669+0000

• Duration: 101 min 15 sec

• Commit: 320a87a

Test stats 🧪

Test	Results
Failed	0
Passed	7164
Skipped	1193
Total	8357

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Test stats 🧪

Test	Results
Failed	0
Passed	7164
Skipped	1193
Total	8357