### What?
Using `create-payload-app` to initialize Payload in an existing Next.js
app **that does not already have Payload installed** overwrites any
existing data in the `.env` and `.env.example` files.
The desired behavior is for Payload variables to get added with no
client data lost.
### How?
Updates `manageEnvFiles` to check for existing `.env / .env.example`
file and appends or creates as necessary.
Adds tests to
`packages/create-payload-app/src/lib/create-project.spec.ts`.
#### Fixes https://github.com/payloadcms/payload/issues/10355
e5b28c98dc