Add endpoint to generate a widget URL

Context

With this endpoint, we are able to add more security to the widget in the future. For example, on the endpoint, we can require an api-key, or access-token in order to make it callable only from supported entities.

TODO

Add a new POST endpoint '/session/create' that can take the following body parameters:

For passing an existing quote to a widget:

{
   "quoteId": "xxx-xxx",
   "walletAddressLocked": "1x0232r23jnjnfjk2n3fjkn434jknf443jnf4j4nf",
   "externalSessionId": "third-party-session-id-1",
   // "externalTransactionId": "third-party-transaction-id-1",
   // "externalCustomerId": "third-party-customer-id-1"
}

For creating a link to the widget that automatically refreshes the quote (without showing the form again)

{
   "inputAmount": "100",
   "sourceCurrencyCode": "USD",
   "destinationCurrencyCodeLocked": "BTC",
   "countryCode": "US",
   "paymentMethod": "CARD",
   "walletAddressLocked": "1x0232r23jnjnfjk2n3fjkn434jknf443jnf4j4nf",
   "externalSessionId": "meldSession1",
   // "externalTransactionId": "meldTransaction1",
   // "externalCustomerId": "meldCustomer1"
}

The response should contain the following:

{
   "widgetUrl": “https://app.vortexfinance.co/widget?rampType=BUY&inputAmount=100&fiat=usd&cryptoLocked=btc&payment=card&walletLocked=1x0232r23jnjnfjk2n3fjkn434jknf443jnf4j4nf
}

or for a widget that does not automatically refresh the quote (pass the quoteId):

{
   "widgetUrl": “https://app.vortexfinance.co/widget?quoteId=xxx-xxx&walletLocked=1x0232r23jnjnfjk2n3fjkn434jknf443jnf4j4nf
}