Update 'llama2' -> 'llama3' in most places (#4116)

* Update 'llama2' -> 'llama3' in most places

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Co-authored-by: Patrick Devine <patrick@infrahq.com>

examples/typescript-simplechat/client.ts

 import * as readline from "readline";
 
-const model = "llama2";
+const model = "llama3";
 type Message = {
   role: "assistant" | "user" | "system";
   content: string;