Missing Java SDK examples

### Description of the feature request:

Its not really a feature request, but I was checking the Gemini docs here https://ai.google.dev/gemini-api/docs/sdks#java and there is a Java example, more of them are here actually.

https://github.com/googleapis/java-genai

### What problem are you trying to solve with this feature?

adding those examples to this repo makes sense, because I was looking around a while, only to find the GitHub link in the docs, which had examples on this path https://github.com/googleapis/java-genai/tree/main/examples

I think some of the main examples should be here, so it's not confusing.

### Any other information you'd like to share?

I'm not sure if this is planned or not, but if it is I can add some examples, like how README.md suggests