Fixing links to examples in `/pkg` examples

[a-poor]

Fixes #177

Removing the following repositories that no longer include a /pkg directory:

• prometheus/prometheus
• minio/minio

Updating the links to the following repositories with renamed main branches:

• jaegertracing/jaeger (renamed master branch to main)
• GoogleContainerTools/kaniko (renamed master branch to main)
• helm/helm (renamed master branch to main)
• grafana/grafana (renamed master branch to main)
• etcd-io/etcd (renamed master branch to main)
• GoogleContainerTools/skaffold (renamed master branch to main)
• knative/serving (renamed master branch to main)
• grafana/loki (renamed master branch to main)
• DataDog/datadog-agent (renamed master branch to main)
• dapr/dapr (renamed master branch to main)
• weaveworks/kured (renamed master branch to main)
• weaveworks/footloose (renamed master branch to main)
• weaveworks/ignite (renamed master branch to main)

[KiruyaMomochi]

Please also update link in /cmd example https://github.com/golang-standards/project-layout/blob/762f59e6e22ea584423f3be8468153e72e9828f3/cmd/README.md?plain=1#L13

• heptio/ark -> vmware-tanzu/velero (created a new branch main)