Add CodeField component

[ukorvl]

closes #152

This diff adds new CodeField component.
Component uses react-codemirror under the hood.
It can be used like so:

import {CodeField} from '@nilfoundation/ui-kit';
import { javascript } from '@codemirror/lang-javascript';
...
<CodeField
  extensions={[javascript({ jsx: true })]}
  code={
    `console.log('js is good')`
  }
  onCopy={({isCopied}) => {isCopied  && window.alert('Copied!')}}
/>