feat: add conditional missing bean

Author: kihwankim

spring-cloud-function-context/src/main/java/org/springframework/cloud/function/context/config/ContextFunctionCatalogAutoConfiguration.java

@@ -181,6 +181,7 @@ protected static class PlainFunctionScanConfiguration {
 	@Configuration(proxyBeanMethods = false)
 	public static class JsonMapperConfiguration {
 		@Bean
+		@ConditionalOnMissingBean(JsonMapper.class)
 		public JsonMapper jsonMapper(ApplicationContext context) {
 			String preferredMapper = context.getEnvironment().getProperty(JSON_MAPPER_PROPERTY);
 			if (StringUtils.hasText(preferredMapper)) {