[Metricbeat] gcp.storage: uniform metricset's fields

[endorama]

What does this PR do?

Uniform gcp.storage fields.yml file.

Why is it important?

As part of #27974 this PR uniform gcp.storage metricset fields.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Author's Checklist

• Run tests TEST_TAGS=gcp MODULE=gcp mage goIntegTest
• updated fields.go before merging

How to test this PR locally

Related issues

• Required for [Metricbeat] gcp: respect Beats naming conventions #27974

Use cases

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[mergify]

This pull request is now in conflicts. Could you fix it? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b gcp/uniform-fields-storage upstream/gcp/uniform-fields-storage
git merge upstream/master
git push upstream gcp/uniform-fields-storage

[mergify]

This pull request is now in conflicts. Could you fix it? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b gcp/uniform-fields-storage upstream/gcp/uniform-fields-storage
git merge upstream/master
git push upstream gcp/uniform-fields-storage