**Description:**
As tool builder I want to read data of all sitelinks of an item so that I can use them in my tool.
**Acceptance criteria:**
- Following endpoint is developed:
GET /entities/items/{item_id}/sitelinks
- Following error cases have to be considered:
<table>
<tr>
<th>
</th>
<th>HTTP response code</th>
<th>response payload</th>
</tr>
<tr>
<td>Item does not exist</td>
<td>404</td>
<td>
`"code": "item-not-found"`
`"message": "Could not find an item with the ID: {item_id}"`
</td>
</tr>
<tr>
<td>Invalid item ID</td>
<td>400</td>
<td>
`"code": "invalid-item-id"`
`"message": "Not a valid item ID: <ITEM_ID>"`
</td>
</tr>
</table>
**Notes:**
- Handle HTTP conditional request headers as in GET /entities/items/{item_id}/statements
- Handle user authentication/authorization like in GET /entities/items/{item_id}/statements
**Possibly relevant pointers:**
- Suggestion in 2020 Wikibase REST API proposal: https://wmde.github.io/wikibase-rest-api-proposal/
- How Wikibase Action API handles this: https://www.wikidata.org/w/api.php?action=wbgetentities&ids=Q42&props=sitelinks