feat(instrumentation-kafkajs): add metrics from messaging semantic conventions

Author: brianphillips

plugins/node/instrumentation-kafkajs/README.md

@@ -53,7 +53,30 @@ You can set the following:
 
 This package uses `@opentelemetry/semantic-conventions` version `1.30+`, which implements Semantic Convention [Version 1.30.0](https://github.com/open-telemetry/semantic-conventions/blob/v1.30.0/docs/README.md)
 
-Attributes collected:
+### Spans Emitted
+
+| KafkaJS Object | Action                     | Span Kind | Span Name                  | Operation Type / Name |
+| -------------- | -------------------------- | --------- | -------------------------- | --------------------- |
+| Consumer       | `eachBatch`                | Client    | `poll <topic-name>`        | `receive` / `poll`    |
+| Consumer       | `eachBatch`, `eachMessage` | Consumer  | `process <topic-name>` [1] | `process` / `process` |
+| Producer       | `send`                     | Producer  | `send <topic-name>`        | `send` / `send`       |
+
+**[1] `process <topic-name>`:** In the context of `eachBatch`, this span will be emitted for each message in the batch but the timing (start, end, duration) will reflect the timing of the batch.
+
+### Metrics Emitted
+
+| KafkaJS Object        | Metric Name                           | Short Description                                            |
+| --------------------- | ------------------------------------- | ------------------------------------------------------------ |
+| Consumer              | `messaging.process.duration`          | Duration of processing operation. [1]                        |
+| Consumer              | `messaging.client.consumed.messages`  | Number of messages that were delivered to the application.   |
+| Consumer and Producer | `messaging.client.operation.duration` | Number of messages that were delivered to the application.   |
+| Producer              | `messaging.client.sent.messages`      | Number of messages producer attempted to send to the broker. |
+
+**[1] `messaging.process.duration`:** In the context of `eachBatch`, this metric will be emitted once for each message but the value reflects the duration of the entire batch.
+
+### Attributes Collected
+
+These attributes are added to both spans and metrics, where possible.
 
 | Attribute                            | Short Description                                                                                                                                                  |
 | ------------------------------------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------ |