[Feature suggestion] Add support for Extension fields (Compose v3.4)

**Is your feature request related to a problem? Please describe.**

With the version 3.4 of compose file was introduce the [Extension fields](https://docs.docker.com/compose/compose-file/compose-file-v3/#extension-fields).

It let you define fragments of configuration that you can reuse in other fields.

Example:
``` compose
version: "3.9"
x-logging:
&default-logging
options:
max-size: '12m'
max-file: '5'
driver: json-file

services:
web:
image: myapp/web:latest
logging: *default-logging
db:
image: mysql:latest
logging: *default-logging
```

**Describe the solution you'd like**
Adding support of Extension fields.

**Describe alternatives you've considered**
Not using Extension fields in compose files. But sometimes, I use compose file written by someone else.