feat: add id_token_signed_response_alg to oidc client

[missedone]

resource "keycloak_openid_client" "oidc_client" {
  realm_id            = data.keycloak_realm.realm.id
  client_id           = "example-oidc-client"
  name                = "Example OIDC Client
  enabled             = true
  ... ...
  // the new property
  id_token_signed_response_alg = "RS256"
}

[missedone]

@mrparkers pls review the PR once you have a chance.

[missedone]

looks like use extra_config can solve the my issue without this PR

  extra_config = {
    "id.token.signed.response.alg" = "RS256"
  }