🌿 ✨ [Scheduled] Update API Spec (#176)

* feat(openapi): add and update schemas for backoff plan, chat completion, and more

* fix(openapi): replace HttpRequest with ApiRequest and add silenceTimeoutMessage

* feat(openapi): add mipOptOut, acknowledgementPhrases, interruptionPhrases, and other improvements to the OpenAPI spec

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Co-authored-by: fern-api[bot] <115122769+fern-api[bot]@users.noreply.github.com>

Author: fern-api[bot]