Add prompt for what package manager Belt should use

[MalcolmTomisin]

Belt offers a flag to define the package manager to use for installing the templates, its not quite clear to the developer when the developer uses belt initiallu.
Having a prompt asking the package manager to use would improve the experience with Belt.

Acceptance Criteria

E.g. When we run npx create-belt-app we want to respond with a prompt listing out the supported package managers Belt uses like:

What package manager would you like Belt to use?

bun
yarn
npm
pnpm