[Discussion] convert all `Option<String>` params to `Option<&str>`

[omid]

Currently, all string params are Option<String> (57 occurrences). What do you think of switching all with Option<&str>?

auth_client: Option<&str>, instead of auth_client: Option<String>,.

[kilork]

I have not touched it as I wanted to keep API same as before, until OpenAPI will show it is stable. Actually seems like now nothing prevents us. Only precondition here is to not introduce breaking change, means it should wait for 25.x version of keycloak.