Support JSON Extractors with Array Indexing in PHP SDK

[elwafa]

Describe the bug
Currently, the Volt-Test Engine supports JSON extraction with array indexing (e.g., data[0].id, data[0].attributes.slug). However, the PHP SDK does not yet have built-in support for handling such JSON paths when interacting with the Volt-Test Engine.

To Reproduce

1. Send a test request using the PHP SDK with a JSON extractor like data[0].id.
2. The SDK does not currently validate this and will throw an exception

Expected behavior
The SDK shloud allow this with using engine version v0.9.1

Environment:

• OS: any
• PHP version all supported
• Version all

Additional context
Since the Volt-Test Engine supports this feature in version 0.9.1, the SDK should:
Implement support for array indexing in the future.