llms: add enum for ernie 4.0 API path

[leehaoze]

PR Checklist

This PR adds a new enumeration value to support the ernie 4.0 model in llms.

The only difference in invoking the ernie 4.0 model compared to previous versions is the API path. This path is defined as a series of enumerations, and I've introduced an additional enum value to accommodate the ernie 4.0 model.

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[tmc]

LGTM