[GCP] Fix loadbalancing_metrics prefix

[gpop63]

What does this PR do?

Loadbalancing dashboards are using gcp.loadbalancing prefix but they need to use gcp.loadbalancing_metrics since the pipeline is using this naming. The fields prefix in fields.yml is also wrong.

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.
• I have verified that Kibana version constraints are current according to guidelines.

Author's Checklist

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How to test this PR locally

Related issues

• Closes [O11y][GCP] Update fields in GCP Load balancing dashboards #7242

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• Start Time: 2023-08-10T08:05:19.251+0000

• Duration: 20 min 36 sec

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[bhapas]

Just a thought : Should this be a minor version bump as there is a change in field name. cc : @andrewkroh

[ishleenk17]

I agree, this should be a minor version bump

[ishleenk17]

@gpop63 What will be the impact on the users using this integration, when they upgrade?
Field names will change for them. This would be a breaking change for them.

[gpop63]

@ishleenk17 won't be a breaking change since fields were still using the correct prefix because of the pipeline (I'll look more into it).

This is before changing fields.yml:

"gcp": {
  "loadbalancing_metrics": {
    "https": {
      "response": {
        "bytes": 893
      }
    }
  },

After the change:

"gcp": {
  "loadbalancing_metrics": {
    "https": {
      "backend_request": {
        "count": 1
      }
    }
  },

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Package gcp - 2.26.0 containing this change is available at https://epr.elastic.co/search?package=gcp