Java: Fixed invalid links in documentation (#3397)

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Updated OpenAI invalid links in Java documentation from
`https://openai.com/api/` to `https://openai.com/product/`.

### Contribution Checklist

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- [x] The code builds clean without any errors or warnings
- [x] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [x] All unit tests pass, and I have added new tests where possible
- [x] I didn't break anyone 😄

java/README.md

@@ -13,7 +13,7 @@ and frameworks.
 ## Get started
 
 To run the LLM prompts and semantic functions in this kernel, make sure you have
-an [Open AI API Key](https://openai.com/api/)
+an [Open AI API Key](https://openai.com/product/)
 or [Azure Open AI service key](https://learn.microsoft.com/azure/cognitive-services/openai/).
 
 ### Requirements

java/samples/sample-code/README.md

@@ -35,7 +35,7 @@ They can then be run by:
 # Configuration
 
 You can define the provider of Open AI by setting the `OPENAI_CLIENT_TYPE`
-property or environment variable to either [`OPENAI`](https://openai.com/api/)
+property or environment variable to either [`OPENAI`](https://openai.com/product/)
 or [`AZURE_OPEN_AI`](https://learn.microsoft.com/azure/cognitive-services/openai/).
 By default, the samples will use the Open AI client.