feat: use new errors pkg in pkg/gameserverset/*

[lacroixthomas]

What type of PR is this?
/kind cleanup

What this PR does / Why we need it:

Use the new error package (https://github.com/agones-dev/agones/blob/main/pkg/util/errors/errors.go) on the pkg/gameserversts/* files

Which issue(s) this PR fixes:
Work on #4510

Did you use AI tools in preparing this PR?:
Y

Special notes for your reviewer:

[agones-bot]

Build Failed 😭

Build Id: b2087f80-8f9e-4094-ab03-47a4e81ccb35

Status: FAILURE

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[agones-bot]

Build Succeeded 🥳

Build Id: 17199340-92b7-42c8-a447-2b9a4f91d288

The following development artifacts have been built, and will exist for the next 30 days:

• image: us-docker.pkg.dev/agones-images/ci/agones-controller:1.61.0-dev-3ae1bfc
• image: us-docker.pkg.dev/agones-images/ci/agones-extensions:1.61.0-dev-3ae1bfc
• image: us-docker.pkg.dev/agones-images/ci/agones-sdk:1.61.0-dev-3ae1bfc-linux
• image: us-docker.pkg.dev/agones-images/ci/agones-ping:1.61.0-dev-3ae1bfc
• image: us-docker.pkg.dev/agones-images/ci/agones-allocator:1.61.0-dev-3ae1bfc
• image: us-docker.pkg.dev/agones-images/ci/agones-processor:1.61.0-dev-3ae1bfc
• Linux C++ SDK (build): agonessdk-1.61.0-dev-3ae1bfc-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.61.0-dev-3ae1bfc.zip

A preview of the website (the last 30 builds are retained):

• https://3ae1bfc-dot-preview-dot-agones-images.appspot.com/

To install this version:

git fetch https://github.com/googleforgames/agones.git pull/4703/head:pr_4703 && git checkout pr_4703
helm install agones ./install/helm/agones --namespace agones-system --set agones.image.registry=us-docker.pkg.dev/agones-images/ci --set agones.image.tag=1.61.0-dev-3ae1bfc

[markmandel]

Just that one docs.go thing, otherwise good to go.

[agones-bot]

Build Succeeded 🥳

Build Id: 23748ba0-e6bf-4e68-af8f-2f688f404904

The following development artifacts have been built, and will exist for the next 30 days:

• image: us-docker.pkg.dev/agones-images/ci/agones-controller:1.61.0-dev-d6ba2e1
• image: us-docker.pkg.dev/agones-images/ci/agones-extensions:1.61.0-dev-d6ba2e1
• image: us-docker.pkg.dev/agones-images/ci/agones-sdk:1.61.0-dev-d6ba2e1-linux
• image: us-docker.pkg.dev/agones-images/ci/agones-ping:1.61.0-dev-d6ba2e1
• image: us-docker.pkg.dev/agones-images/ci/agones-allocator:1.61.0-dev-d6ba2e1
• image: us-docker.pkg.dev/agones-images/ci/agones-processor:1.61.0-dev-d6ba2e1
• Linux C++ SDK (build): agonessdk-1.61.0-dev-d6ba2e1-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.61.0-dev-d6ba2e1.zip

A preview of the website (the last 30 builds are retained):

• https://d6ba2e1-dot-preview-dot-agones-images.appspot.com/

To install this version:

git fetch https://github.com/googleforgames/agones.git pull/4703/head:pr_4703 && git checkout pr_4703
helm install agones ./install/helm/agones --namespace agones-system --set agones.image.registry=us-docker.pkg.dev/agones-images/ci --set agones.image.tag=1.61.0-dev-d6ba2e1

[agones-bot]

Build Failed 😭

Build Id: d4bb0d08-966d-4abf-97f6-f8d5a6db4016

Status: FAILURE

• Cloud Build view
• Cloud Build log download

To get permission to view the Cloud Build view, join the agones-discuss Google Group.