[Feature] Long syntax for images names

Description

I am currently building & running images in CI using this pattern:

1. compose file:

services:
  my:
    image: myimage:${VERSION}
    build:
      args:
        VERSION: ${VERSION}
      tags:
        - myimage:${VERSION}
        - myimage:latest

2. .env file:

VERSION=1.0.0

Then I use a (renovate) bot to bump the version number automatically in my CI whenever the upstream package is updated.

Ideally, I would prefer putting the version number in the compose file using an extension & anchor, and then use the version number later in the compose file using aliases. But I can't because I have to "compute" the full image name from the version anchor, and I can't find a way to do that.

In fact, I would like to do something like this:

x-version: &version 1.0.0

services:
  my:
    image:
      name: myimage
      tag: *version
    build:
      args:
        VERSION: *version
      tags:
        - name: myimage
          tag: *version
        - name: myimage
          tag: latest

Note 1: not sure about if the attribute name is named appropriately, maybe use repository or something else?
Note 2: in fact the same problem occur for all the other "composite" fields that don't have long syntax

The end purpose is to have a self-contained compose file that can be easily updated by my "dependency update" bot.

The issue mentions only the Compose file and .env file; it names no implementation files or tests. Start by reviewing how Compose currently parses image and build fields, then compare existing composite-field syntax with the proposed anchor and alias form. Done means the long syntax and its behavior are specified, implemented, and covered by tests.