[0.34.0-dlc] Fix typo in _extract_lora_adapter function

[xyang16]

Description

Brief description of what this PR is about

• Fix typo in _extract_lora_adapter function. The key should be "adapters", see https://github.com/deepjavalibrary/djl-serving/blob/master/serving/docs/adapters.md#recommended-adapters-parameter-calling

Type of change

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• Bug fix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

Checklist:

• Please add the link of Integration Tests Executor run with related tests.
• Have you manually built the docker image and verify the change?
• Have you run related tests? Check how to set up the test environment here; One example would be pytest tests.py -k "TestCorrectnessLmiDist" -m "lmi_dist"
• Have you added tests that prove your fix is effective or that this feature works?
• Has code been commented, particularly in hard-to-understand areas?
• Have you made corresponding changes to the documentation?

Feature/Issue validation/testing

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• Test A
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[Lokiiiiii]

Are we making a patch release of v16 ? Without this fix, Lora CX is essentially broken I believe ?

[Lokiiiiii]

Can we accept both "adapter" or "adapters" with a defined preference and warning ?

I worry this will break CX for customers who have already started using "adapter"

[xyang16]

For sagemaker users, they always use SAGEMAKER_ADAPTER_IDENTIFIER_HEADER, adapters in the payload is a legacy behavior.