Allow client to close the agent connection (#209)

## Description

Exposes `agent.close()` method.

## Motivation and Context

This allows to close the agent.

## Documentation impact

- [x] Documentation update required
- [ ] Documentation updated [in another PR](_)
- [ ] No documentation update required

## Types of changes

- [x] Bug fix (non-breaking change which fixes an issue)
- [x] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to
      not work as expected)

Author: czerwiukk

packages/js-server-sdk/src/agent.ts

@@ -110,6 +110,10 @@ export class FishjamAgent extends (EventEmitter as new () => TypedEmitter<AgentE
     this.client.send(trackData);
   }
 
+  public disconnect(): void {
+    this.client.close();
+  }
+
   private dispatchNotification(message: MessageEvent) {
     try {
       const data = new Uint8Array(message.data);