Migrate dagger.#Secret and dagger.#Stream to new format

- Refactored to keep every transformation of built-in types (e.g. FS,
  Secret, etc) to/from CUE in the same place (plancontext)
- dagger.#Service and dagger.#Secret are now following the new FS-like format
  (e.g. `_service: id: string`)
- Backward compatibility
- dagger.#Stream is now an alias for dagger.#Service

Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>

docs/reference/dagger/README.md

@@ -56,6 +56,18 @@ _No input._
 
 _No output._
 
+## dagger.#Service
+
+A reference to a network service endpoint, for example:  - A TCP or UDP port  - A unix or npipe socket  - An HTTPS endpoint
+
+### dagger.#Service Inputs
+
+_No input._
+
+### dagger.#Service Outputs
+
+_No output._
+
 ## dagger.#Stream
 
 Dagger stream. Can be mounted as a UNIX socket.