[CLI] Added Convex + Better Auth in the auth packages

[DaveVaval]

Description

• Added Convex + Better Auth in the cli.
• Adapted the base, react-navigation and expo-router templates respectively with the convex client provider.

Motivation and Context

• As Convex is gaining is popularity as a backend solution, and Better Auth as a free open source auth solution, I took the initiative to integrate Convex + Better Auth in the cli.

How Has This Been Tested?

• Manually tested these cli configurations on a physical device:
  npx rn-new@latest my-expo-app --expo-router --nativewind --convex --bun
npx rn-new@latest my-expo-app --react-navigation --nativewind --convex --bun
npx rn-new@latest my-expo-app --nativewind --convex --bun

Screenshots (if appropriate):