[GCP] Fix loadbalancing_metrics prefix

[ghost]

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

• [ ]

How to test this PR locally

Related issues

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

Screenshots

[elasticmachine]

💚 Build Succeeded

the below badges are clickable and redirect to their specific view in the CI or DOCS

Expand to view the summary

Build stats

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

• Duration: 20 min 36 sec

Test stats 🧪

Test	Results
Failed	0
Passed	65
Skipped	0
Total	65

🤖 GitHub comments

Expand to view the GitHub comments

To re-run your PR in the CI, just comment with:

• /test : Re-trigger the build.

[elasticmachine]

🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (6/6)	💚
Files	100.0% (6/6)	💚
Classes	100.0% (6/6)	💚
Methods	87.826% (101/115)	👎 -12.174
Lines	96.0% (1464/1525)	👍 0.259
Conditionals	100.0% (0/0)	💚

[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.

[ghost]

@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
      }
    }
  },

[elasticmachine]

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