Add local composer cache

[andypost]

Alternative to #278

Just keeps changes smaller, the .cache dir already exists if database defined or will be created by composer on first run

[andypost]

Composer 1 and 2 has different defaults for cache dir (~/.composer/cache vs ~/.cache/composer)

https://github.com/composer/composer/blob/2.0.0-RC2/doc/03-cli.md#composer_home

By default, it points to C:\Users<user>\AppData\Roaming\Composer on Windows and /Users//.composer on macOS. On *nix systems that follow the XDG Base Directory Specifications, it points to $XDG_CONFIG_HOME/composer. On other *nix systems, it points to /home//.composer.

Also each php container needs own global set of packages so we can't share its home

[andypost]

For core development I'm using local mounts

    volumes:
      - ./:/var/www/html/web
      - /home/andypost/.cache/composer:/home/www-data/.composer/cache

[davidferlay]

For core development I'm using local mounts

    volumes:
      - ./:/var/www/html/web
      - /home/andypost/.cache/composer:/home/www-data/.composer/cache

That's cool, would $USER variable work here ?
- /home/$USER/.cache/composer:/home/www-data/.composer/cache

[andypost]

I'm sure we can't bet on it as every OS it different locally https://github.com/composer/composer/blob/2.0.0-RC2/doc/03-cli.md#composer_home

So local cache place is user's preference, maybe example of it helpful, thanks will update asap

That's cool, would $USER variable work here ?
- /home/$USER/.cache/composer:/home/www-data/.composer/cache

[andypost]

Still looks more viable to use https://github.com/composer/composer/blob/2.0/doc/03-cli.md#composer_cache_dir to share only cache directory