Schema Events

### Search before asking

- [X] I searched in the [issues](https://github.com/apache/pulsar/issues) and found nothing similar.

### Motivation

Available in other streaming systems, when a schema is created, updated, versioned, or deleted, an event should be created. That event could go to a schema-changes topic, a log file, an external system, or an external metric.

When a change happens, an audit record should be produced. This could be used to populate a downstream system, database, data auditing system, or data provenance/lineage use cases.

The way NiFi produces provenance records at each change of data is really inspiring.

### Solution

When a change happens send it to a system topic.

Is this done during geo-replication now?

### Alternatives

_No response_

### Anything else?

_No response_

### Are you willing to submit a PR?

- [ ] I'm willing to submit a PR!

The issue names no files, tests, or entry points. Start by reviewing Pulsar's schema-change handling and system-topic design, then clarify which schema operations, event destinations, and completion tests are required before implementation.

Written by the indexing model from the issue text.