fix: support multiline descriptions

[shenbenson]

Changes are verified through the added test and a manual diff of the before and after wallet-platform.yaml

Partial diff output:

...
1397c1467,1471
<                   description: Number of confirmations before triggering the webhook. If 0 or unspecified, requests will be sent to the callback endpoint when the transfer is first seen and when it is confirmed.
---
>                   description: |-
>                     Number of confirmations before triggering the webhook. If 0 or unspecified,
> 
>                     requests will be sent to the callback endpoint when the transfer is first
>                     seen and when it is confirmed.
1402c1476,1479
<                   description: Triggers on coin transfers and token transfers for ETH and Stellar. Must be set to true to receive webhooks for Trade accounts.
---
>                   description: |-
>                     Triggers on coin transfers and token transfers for ETH and Stellar.
> 
>                     Must be set to true to receive webhooks for Trade accounts.
...

Also verified changes look good in ReadMe: https://developers.bitgo.com/v1.0_benson-test/reference/v2accesstokenadd#/

Before	After

Ticket: DX-1136