Create Composer 2 version for both Dockerfile and Dockerfile9

[isholgueras]

Is your feature request related to a problem? Please describe.
The current images only support Composer 1, and even with hirak/prestissimo, the speed of dependency calculation and download are not comparable with Composer 2.

Describe the solution you'd like
I think this images should support Composer 2, but keeping Composer 1 to avoid breaking compatibility with existing services using the current images.

Describe alternatives you've considered
The clearer workaround, meanwhile, is to update composer and remove hirak/prestissimo on the very first step with the following:

      - run:
          name: Update Composer to version 2
          command: |
            set -eux
            composer global remove hirak/prestissimo
            composer self-update

This should update the image to Composer 2, removing hirak/prestissimo, until there is an alternative image using Composer 2.

Additional context
After a few months, Composer 2 still throw some issues in projects with Composer 1 dependencies. One example are phpro/grumphp:0.16.
The upgrade from Composer 1 to Composer 2 is not trivial and easy in some cases.
There should be, in my opinion, a clear distinction between the images running composer 1, the current ones, and the new images running composer 2, to avoid breaking compatibility with existing projects.

[salvamomo]

Maybe use semver and add to the README that the new major version supports Composer 2 only?

[eojthebrave]

I don't really have much to add here other than +1 for using semver and building some images with Composer 2 installed in them. And if there's anything I can do help make that happen let me know!

[davereid-pfg]

At this point I think Composer 2 had resolved most of the issues with projects, I would prefer to have it updated by default.

[erikseifert]

    - set -eux
    - composer global remove hirak/prestissimo
    - composer self-update --2

Update to composer 2

[fjgarlin]

I needed to force it in some steps here: #79

I think we are at a point where we should just use composer 2 in the images. I'm actually creating a follow up issue because it's not just composer, it's the PHP version, the node version, etc.

[juampynr]

This was done at #81.