Add client_id to logout url

[claudiunicolaa]

Description

In Keycloak 19 was added support for client_id as described in the OIDC RP-Initiated specification.
More details could be found here keycloak/keycloak#12002 (comment)

At this moment the library does not offer support for setting the client_id in the logout URL and the post_logout_redirect_uri query param is set only if idTokenHint function param is set.

Discussion

No response

Motivation

The library should match the Keycloak Server capabilities.

Details

The logout function should look like this

Keycloak.prototype.logoutUrl = function (redirectUrl, idTokenHint) {
    const url = new URL(this.config.realmUrl + '/protocol/openid-connect/logout')

    url.searchParams.set('client_id', this.config.clientId)

    if (redirectUrl) {
      url.searchParams.set('post_logout_redirect_uri', redirectUrl)
    }
 
    if (idTokenHint) {
      url.searchParams.set('id_token_hint', idTokenHint)
    }

    return url.toString()
}

A part of the above implementation is already done #420.

[claudiunicolaa]

I'm happy to create a PR for it, but first I'm waiting for a maintainer to take a look and validate that my idea looks good.