use a global Composer installation
feature #4173 use a global Composer installation (xabbuh)

This PR was merged into the 2.3 branch.

Discussion
----------

use a global Composer installation

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets | #4170

This pull request replaces all mentions of local Composer installations, but uses a gobal Composer installation instead.

**Note:** This should be considered on hold and not be merged until we have an agreement on this in #4170.

Commits
-------

9ab1c56 use a global Composer installation