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

[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/fleetautoscalers/* 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: 97b67311-ec0b-4f8d-a0d5-e500c478a531

Status: FAILURE

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[agones-bot]

Build Succeeded 🥳

Build Id: bbc66781-3741-4c34-85fc-f11db9449778

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-dc7cf08
• image: us-docker.pkg.dev/agones-images/ci/agones-extensions:1.61.0-dev-dc7cf08
• image: us-docker.pkg.dev/agones-images/ci/agones-sdk:1.61.0-dev-dc7cf08-linux
• image: us-docker.pkg.dev/agones-images/ci/agones-ping:1.61.0-dev-dc7cf08
• image: us-docker.pkg.dev/agones-images/ci/agones-allocator:1.61.0-dev-dc7cf08
• image: us-docker.pkg.dev/agones-images/ci/agones-processor:1.61.0-dev-dc7cf08
• Linux C++ SDK (build): agonessdk-1.61.0-dev-dc7cf08-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.61.0-dev-dc7cf08.zip

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

• https://dc7cf08-dot-preview-dot-agones-images.appspot.com/

To install this version:

git fetch https://github.com/googleforgames/agones.git pull/4711/head:pr_4711 && git checkout pr_4711
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-dc7cf08

[agones-bot]

Build Succeeded 🥳

Build Id: 1c2bc5b2-1675-4ce1-ad02-977bc7a04dea

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-9884178
• image: us-docker.pkg.dev/agones-images/ci/agones-extensions:1.61.0-dev-9884178
• image: us-docker.pkg.dev/agones-images/ci/agones-sdk:1.61.0-dev-9884178-linux
• image: us-docker.pkg.dev/agones-images/ci/agones-ping:1.61.0-dev-9884178
• image: us-docker.pkg.dev/agones-images/ci/agones-allocator:1.61.0-dev-9884178
• image: us-docker.pkg.dev/agones-images/ci/agones-processor:1.61.0-dev-9884178
• Linux C++ SDK (build): agonessdk-1.61.0-dev-9884178-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.61.0-dev-9884178.zip

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

• https://9884178-dot-preview-dot-agones-images.appspot.com/

To install this version:

git fetch https://github.com/googleforgames/agones.git pull/4711/head:pr_4711 && git checkout pr_4711
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-9884178

[agones-bot]

Build Succeeded 🥳

Build Id: 842cf071-8ce6-4fe5-a766-66f41b4bad0a

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-61c6cc6
• image: us-docker.pkg.dev/agones-images/ci/agones-extensions:1.61.0-dev-61c6cc6
• image: us-docker.pkg.dev/agones-images/ci/agones-sdk:1.61.0-dev-61c6cc6-linux
• image: us-docker.pkg.dev/agones-images/ci/agones-ping:1.61.0-dev-61c6cc6
• image: us-docker.pkg.dev/agones-images/ci/agones-allocator:1.61.0-dev-61c6cc6
• image: us-docker.pkg.dev/agones-images/ci/agones-processor:1.61.0-dev-61c6cc6
• Linux C++ SDK (build): agonessdk-1.61.0-dev-61c6cc6-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.61.0-dev-61c6cc6.zip

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

• https://61c6cc6-dot-preview-dot-agones-images.appspot.com/

To install this version:

git fetch https://github.com/googleforgames/agones.git pull/4711/head:pr_4711 && git checkout pr_4711
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-61c6cc6