Add alinea to server-external-packages.json (#55006)
### What?
Adds `@alinea/generated` to the external package list
### Why?
[`Alinea`](https://github.com/alineacms/alinea) generates this package
at build time and it should not end up in a cache (much like the
`@prisma/client` package)
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Co-authored-by: JJ Kasper <jj@jjsweb.site>
Co-authored-by: Tim Neutkens <tim@timneutkens.nl>
