Add config property for webflux codec maxInMemorySize

This commit creates a new configuration property
`spring.codec.max-in-memory-size` which configures the maximum
amount of data to be buffered in memory by codecs (both client and
server).

This property has no default value - it will let Spring Framework handle
the default behavior, currently enforcing a 256KB for provided codecs.

Fixes gh-18828

spring-boot-project/spring-boot-docs/src/main/asciidoc/spring-boot-features.adoc

@@ -2538,8 +2538,9 @@ If you want to take complete control of Spring WebFlux, you can add your own `@C
 Spring WebFlux uses the `HttpMessageReader` and `HttpMessageWriter` interfaces to convert HTTP requests and responses.
 They are configured with `CodecConfigurer` to have sensible defaults by looking at the libraries available in your classpath.
 
-Spring Boot applies further customization by using `CodecCustomizer` instances.
-For example, `spring.jackson.*` configuration keys are applied to the Jackson codec.
+Spring Boot provides dedicated configuration properties for codecs, `+spring.codec.*+`.
+It also applies further customization by using `CodecCustomizer` instances.
+For example, `+spring.jackson.*+` configuration keys are applied to the Jackson codec.
 
 If you need to add or customize codecs, you can create a custom `CodecCustomizer` component, as shown in the following example:
 
@@ -2554,7 +2555,7 @@ If you need to add or customize codecs, you can create a custom `CodecCustomizer
 		public CodecCustomizer myCodecCustomizer() {
 			return codecConfigurer -> {
 				// ...
-			}
+			};
 		}
 
 	}

spring-boot-project/spring-boot-docs/src/main/groovy/generateConfigurationPropertyTables.groovy

@@ -24,7 +24,7 @@ def generateConfigMetadataDocumentation() {
 		builder
 				.addSection("core")
 					.withKeyPrefixes("debug", "trace", "logging", "spring.aop", "spring.application",
-						"spring.autoconfigure", "spring.banner", "spring.beaninfo", "spring.config",
+						"spring.autoconfigure", "spring.banner", "spring.beaninfo", "spring.codec", "spring.config",
 						"spring.info", "spring.jmx", "spring.main", "spring.messages", "spring.pid",
 						"spring.profiles", "spring.quartz", "spring.reactor", "spring.task",
 						"spring.mandatory-file-encoding", "info", "spring.output.ansi.enabled")