Proposal: Change default route to /v1/chat/completions

[git-jxj]

Is your feature request related to a problem? Please describe.

"I propose setting /v1/chat/completions as the default route. This would align the tool with current industry best practices, where the chat
completions endpoint is the definitive standard. It streamlines the setup for the vast majority of users, while ensuring backward compatibility is
maintained for the minority who rely on the legacy /v1/completions endpoint, as they can opt-in to the old behavior by setting
GUIDELLM__PREFERRED_ROUTE="text_completions"."

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[sjmonson]

Won't Do. chat/completions adds extra tokens to the prompt which bias testing. Additionally we rely on tunables which are not officially part of the chat/completions spec. We only support chat/completions for when the text completions is unavailable.