Add OidcClientConfig Grant getter and setter

[sberyozkin]

Minor OidcClientConfig update related to this https://stackoverflow.com/questions/70594412/quarkus-oidc-client-grant-configuration question

[r00ta]

Hi @sberyozkin , thank you very much for the PR!
One last thing I faced is that the mapping between the config string and the enum has to be done somehow on client side. I implemented this https://github.com/5733d9e2be6485d52ffa08870cabdee0/sandbox/blob/main/infra/src/main/java/com/redhat/service/bridge/infra/auth/OidcClientConfigUtils.java but it might be useful if it's the library to expose it