Remove use of github.com/pkg/errors

[AlexanderYastrebov]

See pkg/errors#245

We can probably replace it by https://pkg.go.dev/errors#Join introduced in 1.20

[AlexanderYastrebov]

After #2492 we still have it as indirect

$ go mod why -m github.com/pkg/errors
# github.com/pkg/errors
github.com/zalando/skipper/tracing/tracers/jaeger
github.com/uber/jaeger-client-go/config
github.com/pkg/errors

Related to #2153 and #2104

[AlexanderYastrebov]

If jaeger dependency is removed then

$ go mod why -m github.com/pkg/errors
# github.com/pkg/errors
github.com/zalando/skipper/net/redistest
github.com/testcontainers/testcontainers-go
github.com/docker/docker/api/types/registry
github.com/pkg/errors

[AlexanderYastrebov]

There are other dependencies, namely OPA, using github.com/pkg/errors:

$ go mod graph | grep github.com/pkg/errors
github.com/zalando/skipper github.com/pkg/errors@v0.9.1
github.com/containerd/containerd@v1.7.4 github.com/pkg/errors@v0.9.1
github.com/dgraph-io/badger/v3@v3.2103.5 github.com/pkg/errors@v0.9.1
github.com/dgraph-io/ristretto@v0.1.1 github.com/pkg/errors@v0.9.1
github.com/open-policy-agent/opa@v0.56.0 github.com/pkg/errors@v0.9.1
github.com/open-policy-agent/opa-envoy-plugin@v0.56.0-envoy github.com/pkg/errors@v0.9.1
github.com/opencontainers/image-spec@v1.1.0-rc4 github.com/pkg/errors@v0.9.1
github.com/testcontainers/testcontainers-go@v0.23.0 github.com/pkg/errors@v0.9.1