Create or update the source connection

curl --request POST \
  --url https://app.vern.so/api/v1/migrations/{migration_id}/source-connection \
  --header 'Content-Type: application/json' \
  --header 'x-api-key: <api-key>' \
  --data '
{
  "source_key": "salesforce",
  "config": {
    "instance_url": "https://acme.my.salesforce.com"
  },
  "selected_streams": [
    "contacts",
    "accounts"
  ],
  "credentials": {
    "client_id": "…",
    "client_secret": "…"
  }
}
'

{
  "source_connection": {
    "id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
    "profile_id": "<string>",
    "source_key": "<string>",
    "name": "<string>",
    "category": "<string>",
    "config": {},
    "selected_streams": [
      "<string>"
    ],
    "stream_state": {},
    "creds_configured": true,
    "bound_source_extractor_id": "<string>",
    "last_snapshot": {},
    "last_sync_at": "2023-11-07T05:31:56Z"
  }
}