[REQ] Support for a oauth access token supplier in Java RestClient clients

[RockyMM]

Is your feature request related to a problem? Please describe.

It would be nice that, similarly to RestTemplate clients (thanks to work done in #19002), that RestClient clients also have a helper method to set the access token supplier, without interating through the authentications object.

Describe the solution you'd like

Continue work in #19943 and add

public void setAccessToken(Supplier<String> tokenSupplier) {
        for (Authentication auth : authentications.values()) {
            if (auth instanceof OAuth) {
                ((OAuth) auth).setAccessToken(tokenSupplier);
                return;
            }
        }
}

to modules/openapi-generator/src/main/resources/Java/libraries/restclient/ApiClient.mustache

Describe alternatives you've considered

Iterate through he authentications object.