JSON creation keyword that adds the string {{value}} to the current JSON List.

Example:

| `Start JSON Object`         |         |
| `Start JSON List`           | names   |
| `Add JSON List String Item` | alvin   |
| `Add JSON List String Item` | shiela  |
| `Add JSON List String Item` | ashier  |
| `End JSON List`             |
| `End JSON Object`           |
| ${jsonString}=                 | `Create JSON String` |

{{jsonString}}:

| {
|    "names": ["alvin", "shiela", "ashier"]
| }
