Consolidated compose.yml files for Dev Container

[cmraible]

ref https://linear.app/ghost/issue/ENG-1785/consolidate-dev-container-composeyml-with-the-root-level-composeyml

• We currently have two compose.yml files:
  • .devcontainer/compose.yml: used for the Dev Container
  • compose.yml: used for local development with docker compose
• The Dev Container compose file does need some additional configuration, but most of this code is duplicated from the root level compose.yml file
• This commit removes this duplication by using both compose files in the Dev Container setup, so it will base the compose configuration on the root level, and then extend it with the Dev Container specific configuration
• This way any updates to the root level compose file will also be available and reflected in the Dev Container setup without having to make the change twice.