🌿 ✨ [Scheduled] Update API Spec (VapiAI#93)

* refactor(openapi): remove CanonicalKnowledgeBase and add OAuth2AuthenticationPlan

* feat(openapi.json): Add Oauth2AuthenticationSession and update XAiCredential

This commit introduces a new object, Oauth2AuthenticationSession, which includes properties for the OAuth2 access token and its expiration. It also updates the XAiCredential schema to include an "authenticationSession" field, providing details about the authentication plan.

* fix(fern/apis/api): add tavus video failure pipeline error code

* fix(fern/apis/api): remove tavus video error from openapi.json

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