Add webhook list command

[joshmgross]

This pulls in the latest version of planetscale-go from planetscale/planetscale-go#276 and implements the webhook list command. Create, delete, update, and test will be implemented in follow-up PRs.

pscale webhook list planetscale -f json
[
  {
    "id": "4h7gbsu2wmsp",
    "url": "<redacted>",
    "secret": "<redacted>",
    "enabled": true,
    "last_sent_result": "200",
    "last_sent_success": true,
    "last_sent_at": "2025-11-26T19:40:55.59Z",
    "created_at": "2023-10-17T17:42:58.012Z",
    "updated_at": "2025-11-26T19:40:55.592Z",
    "events": [
      "deploy_request.closed",
      "deploy_request.errored",
      "deploy_request.in_progress",
      "deploy_request.opened",
      "deploy_request.queued",
      "deploy_request.reverted",
      "deploy_request.schema_applied"
    ]
  },
  {
    "id": "uj6gtktlj7m2",
    "url": "<redacted>",
    "secret": "<redacted>",
    "enabled": true,
    "last_sent_result": "200",
    "last_sent_success": true,
    "last_sent_at": "2025-11-19T22:18:23.358Z",
    "created_at": "2025-08-07T04:43:30.814Z",
    "updated_at": "2025-11-19T22:18:23.359Z",
    "events": [
      "branch.schema_recommendation"
    ]
  }
]

(<redacted> was added by me, not part of the actual response).