public static ApplicationId application() {
        return ApplicationId.from(requireNonBlankProperty("tenant"),
                                  requireNonBlankProperty("application"),
                                  requireNonBlankProperty("instance"));
    }
Returns the relevant application ID. This is the 'tenant', 'application' and 'instance' properties.
The instance defaults to the user name of the current user, if not explicitly set.
hosted-api/src/main/java/ai/vespa/hosted/api/Properties.java