Add proper message when wrong log level is sent

[eddumelendez]

Previously, bad request with no reason was included in the response.
This commit introduces the reason when invalid log level is sent in the
request.

See gh-10568

[wilkinsona]

I've opened #10618 to do something more general purpose in the web endpoint infrastructure for 2.0.

[UtsaVakani]

Hello,
I am using 2.1.3.RELEASE version and still getting 500 on giving improper configuredLevel in POST payload for /loggers endpoint ...

[wilkinsona]

@UtsaVakani You should get a 400 for an unrecognised configuredLevel. We have an integration test that verifies that this is the case:

spring-boot/spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/logging/LoggersEndpointWebIntegrationTests.java

Lines 122 to 129 in f15e04b

	@Test
	public void setLoggerWithWrongLogLevelResultInBadRequestResponse() {
	client.post().uri("/actuator/loggers/ROOT")
	.contentType(MediaType.APPLICATION_JSON)
	.syncBody(Collections.singletonMap("configuredLevel", "other")).exchange()
	.expectStatus().isBadRequest();
	verifyZeroInteractions(this.loggingSystem);
	}

If you are seeing different behaviour, please open a new issue with a small sample project that reproduces the 500 response.