acquire fn public in admin token retriever

[ovnicraft]

We need to get the admin token for service accounts.

as developer i would like to do:

let retriever = KeycloakServiceAccountAdminTokenRetriever::create(
    client_id,
    client_secret,
    realm,
    client,
};
let admin_token = retriever.acquire(&url).await;

[kilork]

I think authorization was never deeply thought in the crate to avoid to much complexity, simplicity here is basically to force users to think about how to do it for their case with minimal example.

If just access_token field is not enough and you really need the whole token, we can of course make it public. @ovnicraft Please comment before the weekend, as I plan to do a release for version 25 of keycloak this week.

[ovnicraft]

Make it public its good enough to use a service account and get token, please make it public.

Good to know to get it on next release.

[kilork]

Okay, also other supplier has acquire method public already, means, this makes this consistent.