[Java SDK] Implement metrics collection and monitoring

**Title:** `[Java SDK] Implement metrics collection and monitoring`

**Description:**
No built-in metrics collection, making production monitoring difficult.

**Proposed Solution:**
```java
// Metrics API
IggyMetrics metrics = client.metrics();
metrics.getMessagesProduced();
metrics.getMessagesConsumed();
metrics.getConsumerLag();

// JMX integration
client.enableJmxMetrics("org.apache.iggy");

// Micrometer support
client.bindTo(meterRegistry);
```

The issue names no files, tests, or Java SDK entry point; start by locating the client implementation and assessing how the proposed IggyMetrics, JMX, and Micrometer APIs would fit. Done means production metrics collection is available through the listed API, with JMX and Micrometer integration as specified.

Written by the indexing model from the issue text.