Add a label property to snippets to override the generated tab label

[jackwakefield]

This allows for custom labels like below

<CodeSnippetWidget
  har={exampleHAR}
  snippets={[
    {
      prismLanguage: "javascript",
      target: "javascript",
      client: "jquery",
      label: "JavaScript (jQuery)"
    },
    {
      prismLanguage: "bash",
      target: "shell",
      client: "curl",
      label: "cURL"
    },
  ]}
/>

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