Allow to change conversation title using REST API endpoint.

The topic is solver in v2.13.

Just did a test and it appear to be working. Here an example of cURL:

curl --location --request PUT 'https://api.intercom.io/conversations/123' \

--header 'Intercom-Version: 2.13' \

--header 'Accept: application/json' \

--header 'Content-Type: application/json' \

--header 'Authorization: Bearer  ·········' \

--data '{

    "title": "New Title",

}'