Allow updateToken() in keycloak-js to be provided a scopes list to do a token exchange.

[Esurnir]

While reading the release note and the documentation for token exchange. I saw that token exchange was disabled for public client because there's a "standard" way to handle token exchange by using a refresh token to alter the scope list. In my current scenario. I want to be able to change a user token's organization by asking a token with "organization:newOrg" as a scope without forcing a new login and forced navigation.