Consistently coerce false to off and true to on where applicable

[wilkinsona]

YAML 1.1 maps off to false. We deal with this in LoggingApplicationListener by coercing false back to LogLevel.OFF:

spring-boot/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/logging/LoggingApplicationListener.java

Lines 363 to 369 in 35a178a

	private LogLevel coerceLogLevel(String level) {
	String trimmedLevel = level.trim();
	if ("false".equalsIgnoreCase(trimmedLevel)) {
	return LogLevel.OFF;
	}
	return LogLevel.valueOf(trimmedLevel.toUpperCase(Locale.ENGLISH));
	}

This allows users to configure logging using logging.level.example.my.package: off in YAML.

We do no perform any coercion when turning the banner off so spring.main.banner-mode: off will fail and spring.main.banner-mode: 'off' has to be used instead.

I think we should consistently allow false to be bound to an enum that would accept off. Perhaps this is something that could be done in the binder rather than as a special case for banner mode.

[wilkinsona]

There's some advice in the docs about turning the banner off that we can remove now.

[romainmoreau]

Since Spring Boot 2.2.0.M5, I have to use logging.level.example.my.package: 'off' instead of logging.level.example.my.package: off which worked with Spring Boot 2.2.0.M4 but is now silently ignored with Spring Boot 2.2.0.M5.
When I read this issue, I understand that it should not be the case, should it?