Define capnp embed expressions through serializeConfig() or capnp-ts

[mootari]

Miniflare exports a serializeConfig helper to generate a binary capnp config from a Config object.

workerd's examples make heavy use of capnp embed expressions, but I can't figure out how to define those via JS. I tried to look through the sources for capnp-ts and capnp but couldn't glean anything from them yet.

My questions are:

1. How can I define an embed expression, either for serializeConfig() or directly via capnp-ts?
2. Would this still embed the file contents directly when compiling the config, or would the file be included at runtime?