Auto-detect package manager based on prefix command

[danstepanov]

Additions

• npx rn-new and npx create-expo-stack should have the project use npm
• yarn dlx rn-new, yarn rn-new, yarn dlx create-expo-stack, and yarn create-expo-stack should have the project use yarn
• pnpm dlx rn-new and pnpm dlx create-expo-stack should have the project use pnpm
• bunx rn-new and bunx create-expo-stack should have the project use bun

Removal (optional)

• Remove the package manager flags