use the v3 engine metadata.json instead of maintaining a local one (#445

)

### What

The v3-engine metadata.json we maintain is this repo keeps getting out
of date.
This PR removes it completely, and uses a configuration that is maintain
in v3 engine instead, which is used in tests, which means it is
maintained.

justfile

@@ -233,7 +233,7 @@ run-engine: start-dependencies
     cargo run \
     --manifest-path {{ HGE_V3_DIR }}/Cargo.toml \
     --bin engine -- \
-    --metadata-path ./static/postgres/chinook-metadata.json \
+    --metadata-path {{ HGE_V3_DIR }}/crates/engine/tests/schema.json \
     --authn-config-path ./static/auth_config.json
 
 # run a standard request to check the service correctly integrates with the engine.