Adds minimal setup for custom eslint rule.

- Introduces a lint rule `jsx-no-ampersands` copied from on `jsx-embed-condition`: https://github.com/yannickcr/eslint-plugin-react/blob/ee232bbaef4fb04740413d5048877559abf06222/lib/rules/jsx-embed-condition.js
- TODO: add tests for `jsx-no-ampersands`
- To use this rule, add the following to `.eslintrc`:
```json
 {
  "plugins": [
   "grailed"
  ],
  "rules": {
   "grailed/jsx-no-ampersands": "warn"
  }
 }
```

Co-authored-by: Bean <10777333+GeneTheBean@users.noreply.github.com>