cargo-progenitor: add pipe support

example:
```sh
echo "openapi: 3.0.3..." | cargo progenitor \
	--input /dev/stdin \
	--output packages/generated/rust \
	--name models \
	--version 0.1.0
```
or without --input at all (read stdin by default)
```sh
echo "openapi: 3.0.3..." | cargo progenitor \
	--output packages/generated/rust \
	--name models \
	--version 0.1.0
```