NullPointerException when using a service that is not a Ns4Kafka instance

[loicgreffier]

In the Kafkactl config, define a service that is not Ns4Kafka:

kafkactl:
  contexts:
  ...
current-namespace: myNamespace
api: https://gitlab.com # Something invalid, but that actually exists
user-token: admin

Run kafkactl auth renew:

It triggers:

java.lang.NullPointerException
	at com.michelin.kafkactl.service.LoginService.login(LoginService.java:150)
	at com.michelin.kafkactl.service.LoginService.doAuthenticate(LoginService.java:84)
	at com.michelin.kafkactl.command.auth.AuthRenew.call(AuthRenew.java:58)
	at com.michelin.kafkactl.command.auth.AuthRenew.call(AuthRenew.java:34)
	at picocli.CommandLine.executeUserObject(CommandLine.java:2031)
	at picocli.CommandLine.access$1500(CommandLine.java:148)
	at picocli.CommandLine$RunLast.executeUserObjectOfLastSubcommandWithSameParent(CommandLine.java:2469)
	at picocli.CommandLine$RunLast.handle(CommandLine.java:2461)
	at picocli.CommandLine$RunLast.handle(CommandLine.java:2423)
	at picocli.CommandLine$AbstractParseResultHandler.execute(CommandLine.java:2277)
	at picocli.CommandLine$RunLast.execute(CommandLine.java:2425)
	at picocli.CommandLine.execute(CommandLine.java:2174)
	at io.micronaut.configuration.picocli.PicocliRunner.execute(PicocliRunner.java:226)
	at io.micronaut.configuration.picocli.PicocliRunner.execute(PicocliRunner.java:188)
	at com.michelin.kafkactl.Kafkactl.main(Kafkactl.java:99)
	at java.base@21.0.9/java.lang.invoke.LambdaForm$DMH/sa346b79c.invokeStaticInit(LambdaForm$DMH)

If the login response is not compliant, it should warn that the configured API is not an Ns4Kafka API.