Support for ThiningLevel

[alexander-schranz]

ThinkingConfig has now a ThinkingLevel: https://ai.google.dev/api/generate-content?hl=de#ThinkingConfig

Related Class: https://github.com/google-gemini-php/client/blob/main/src/Data/ThinkingConfig.php

[aydinfatih]

#161

https://github.com/google-gemini-php/client/releases/tag/2.7.3