feat: stop using github.com/pkg/errors in examples/*

[lacroixthomas]

What type of PR is this?
/kind cleanup

What this PR does / Why we need it:

Stop using github.com/pkg/errors in examples/*, uses either go std errors or fmt.Errorf when needed

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 Succeeded 🥳

Build Id: e728a468-9465-469f-b034-578c0569c877

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-f845c47
• image: us-docker.pkg.dev/agones-images/ci/agones-extensions:1.61.0-dev-f845c47
• image: us-docker.pkg.dev/agones-images/ci/agones-sdk:1.61.0-dev-f845c47-linux
• image: us-docker.pkg.dev/agones-images/ci/agones-ping:1.61.0-dev-f845c47
• image: us-docker.pkg.dev/agones-images/ci/agones-allocator:1.61.0-dev-f845c47
• image: us-docker.pkg.dev/agones-images/ci/agones-processor:1.61.0-dev-f845c47
• Linux C++ SDK (build): agonessdk-1.61.0-dev-f845c47-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.61.0-dev-f845c47.zip

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

• https://f845c47-dot-preview-dot-agones-images.appspot.com/

To install this version:

git fetch https://github.com/googleforgames/agones.git pull/4723/head:pr_4723 && git checkout pr_4723
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-f845c47