feat: Allow path starting with slash

[Azhovan]

Problem :
I started using Transformer Configurations with the following spec:

directory structure:

├── kustomization.yaml
├── namespace.yaml
└── resource.yaml

➜ cat kustomization.yaml

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
namespace: ns1

resources:
- resource.yaml

configurations:
  - namespace.yaml

➜ cat resource.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: web-1
  name: web-1
spec:
  replicas: 1
  selector:
    matchLabels:
      app: web-1
  strategy: {}
  template:
    metadata:
      labels:
        app: web-1
    spec:
      containers:
      - image: nginx
        name: nginx

➜ cat namespace.yaml

namespace:
  - kind: Deployment
    path: metadata/namespace
    create: true

I noticed when path in namespace.yaml starts with a slash i.e /metadata/namespace PathSplitter function returns a slice of strings where first element is an empty string, causing kustomize to return an error like this, when I ran:
kustomize build .
in root of the directory.

Error: namespace transformation failed: considering field '/metadata/namespace' 
of object Deployment.v1.apps/web-1.ns1: cannot set or create an empty field name

handling this forward slash at the beginning of a path seems to make working with kustomize easier

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: Azhovan / name: Jabar Asadi (368697f)

[k8s-ci-robot]

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[k8s-ci-robot]

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[Azhovan]

@KnVerey @natasha41575
do you find this change relevant?

[Azhovan]

/assign @phanimarupaka

[Azhovan]

@phanimarupaka @mortent
Kindly a reminder,
If this is not relevant, let's close it?

[KnVerey]

/ok-to-test

[natasha41575]

/lgtm

[KnVerey]

/approve

Thanks for the contribution!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Azhovan, KnVerey

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