GH-3779: Fix KafkaTemplate from hiding error when starting observation

Fixes: #3779

This fixes that exceptions thrown from `observation.start()` are hidden by `KafkaTemplate` throwing a new exception due to registering observation error without successfully starting the observation.

Signed-off-by: Christian Fredriksson <[email protected]>

**Auto-cherry-pick to `3.3.x` & `3.2.x`**

Author: cfredri4

spring-kafka/src/main/java/org/springframework/kafka/core/KafkaTemplate.java

@@ -805,8 +805,8 @@ private CompletableFuture<SendResult<K, V>> observeSend(final ProducerRecord<K,
 				this.observationConvention, DefaultKafkaTemplateObservationConvention.INSTANCE,
 				() -> new KafkaRecordSenderContext(producerRecord, this.beanName, this::clusterId),
 				this.observationRegistry);
+		observation.start();
 		try {
-			observation.start();
 			try (Observation.Scope ignored = observation.openScope()) {
 				return doSend(producerRecord, observation);
 			}