Add Okta Auth0 as OIDC provider

[hosuaby]

This PR adds a provider for Okta Auth0. Auth0 itself is OIDC OP, so also works with discovery. This value this PR brings is to enforce the user to provide a mandatory parameter "audience." The following notations are equivalent:

With OIDC discovery

        WebClient client = WebClient.create(vertx, new WebClientOptions());
        String site = "https://{tenant}.auth0.com";
        OpenIDConnectAuth.discover(
                        vertx,
                        new OAuth2Options()
                                .setSite(site)
                                .setClientId(Auth0Credentials.CLIENT_ID)
                                .setClientSecret(Auth0Credentials.CLIENT_SECRET)
                                .setTenant(Auth0Credentials.TENANT)
                                .setExtraParameters(new JsonObject()
                                        .put("audience", Auth0Credentials.AUDIENCE)))
                .onSuccess(oauth2 -> {
                    Oauth2Credentials credentials = new Oauth2Credentials()
                            .setUsername(Auth0Credentials.CLIENT_ID)
                            .setPassword(Auth0Credentials.CLIENT_SECRET)
                            .setFlow(OAuth2FlowType.CLIENT);
                    OAuth2WebClient authClient = OAuth2WebClient
                            .create(client, oauth2)
                            .withCredentials(credentials);

                    // Here goes an authenticated call
                })

With factory method

        WebClient client = WebClient.create(vertx, new WebClientOptions());
        OAuth2Auth oauth2 = Auth0Auth.create(
                vertx,
                Auth0Credentials.CLIENT_ID,
                Auth0Credentials.CLIENT_SECRET,
                Auth0Credentials.TENANT,
                Auth0Credentials.AUDIENCE);

        Oauth2Credentials credentials = new Oauth2Credentials()
                .setUsername(Auth0Credentials.CLIENT_ID)
                .setPassword(Auth0Credentials.CLIENT_SECRET)
                .setFlow(OAuth2FlowType.CLIENT);
        OAuth2WebClient authClient = OAuth2WebClient
                .create(client, oauth2)
                .withCredentials(credentials);

         // Here goes an authenticated call