[exporter/datadogexporter] Add config example for kafka metrics (#30752)

**Description:** 
This PR adds an example on how to configure the OTel collector to pull
kafka metrics.

**Link to tracking Issue:** <Issue number if applicable>

**Testing:** <Describe what testing was performed and which tests were
added.>

**Documentation:** <Describe the documentation added.>

exporter/datadogexporter/examples/kafka.yaml

@@ -0,0 +1,61 @@
+receivers:
+ otlp:
+ protocols:
+ http:
+ endpoint: "localhost:4318"
+ grpc:
+ endpoint: "localhost:4317"
+ filelog:
+ include_file_path: true
+ poll_interval: 500ms
+ include:
+ - /var/log/kafka/server.log
+ operators:
+ - type: json_parser
+ kafkametrics:
+ brokers: "${env:KAFKA_BROKER_ADDRESS}"
+ protocol_version: 2.0.0
+ scrapers:
+ - brokers
+ - topics
+ - consumers
+ jmx:
+ jar_path: /path/to/opentelemetry-jmx-metrics.jar
+ endpoint: ${env:KAFKA_BROKER_JMX_ADDRESS}
+ target_system: kafka,jvm
+ jmx/consumer:
+ jar_path: /path/to/opentelemetry-jmx-metrics.jar
+ endpoint: ${env:KAFKA_CONSUMER_JMX_ADDRESS}
+ target_system: kafka-consumer
+ jmx/producer:
+ jar_path: /path/to/opentelemetry-jmx-metrics.jar
+ endpoint: ${env:KAFKA_PRODUCER_JMX_ADDRESS}
+ target_system: kafka-producer
+
+processors:
+ batch:
+ send_batch_max_size: 1000
+ send_batch_size: 100
+ timeout: 10s
+ attributes:
+ actions:
+ - key: ddtags
+ value: "source:kafka"
+ action: insert
+
+exporters:
+ datadog:
+ api:
+ site: ${env:DD_SITE}
+ key: ${env:DD_API_KEY}
+
+service:
+ pipelines:
+ metrics:
+ receivers: [otlp, kafkametrics, jmx, jmx/consumer, jmx/producer]
+ processors: [batch]
+ exporters: [datadog]
+ logs:
+ receivers: [otlp, filelog]
+ processors: [batch, attributes]
+ exporters: [datadog]

exporter/datadogexporter/examples_test.go

@@ -41,6 +41,10 @@ func TestExamples(t *testing.T) {
  files, err := os.ReadDir(folder)
  require.NoError(t, err)
  for _, f := range files {
+ if f.Name() == "kafka.yaml" {
+ // skip validation, as it requires jar file.
+ continue
+ }
  if f.IsDir() {
  continue
  }