Implement recommendations around client_id

[michielbdejong]

@dmitrizagidulin I had a look at https://github.com/solid/oidc-auth-manager/blob/80860f88c5b160e9b9290455b066063ba40acd9e/src/handlers/login-consent-request.js but couldn't find the line where "the IdP to generate a random client_id" happens, in any case, this is a ticket to track implementation of recommendations from solid/webid-oidc-spec#12