feat: use correct pkg manager when creating keystone app

[iamandrewluca]

Depending on what package manager tools were used, that package manager will be used.

Below package managers were tested, and are working:

• NPM (npx, npm exec, npm init, npm create)
• Yarn (yarn dlx, yarn create)
• PNPm (pnpm exec, pnpm create, pnpm dlx)
• Bun (bun create, bun init)

Closes #413

[iamandrewluca]

This is an adaptation of https://github.com/vitejs/vite/blob/2d50be2a5424e4f4c22774652ed313d2a232f8af/packages/create-vite/src/index.ts#L538-L546

[dcousens]

Hi @iamandrewluca,
Sorry I didn't get to reviewing this pull request.
I think I want to move this repository into https://github.com/keystonejs/keystone/ soon, as it's really difficult to keep the create-keystone-app up to date when it isn't synchronised with our monorepo.

[iamandrewluca]

Hey @dcousens, I understand the pain of keeping it up to date. I'm here if you need any help from my side.

[iamandrewluca]

Hey @dcousens, taking into consideration what you said about create-keystone-app above, are you also considering in the future releasing all mono-repo packages under the same version to keep them all in sync?

e.g.

@keystone-6/auth@7.1
@keystone-6/core@7.1