Allow composer location to be configured via the UI

Problem/Motivation

Package manager allows you to configure composer's location via package_manager.settings::executables.composer but there is no UI for this. I've been setting up Drupal CMS on cheap hosting (hostinger) and trying to enable automatic updates. The first problem I had was that the composer it initially found was out of date. Hostinger currently makes composer 1 and composer 2 available. Composer 1 is composer and Composer 2 is composer2. Potentially we could consider looking for both composer and composer2 but even when I changed it to the composer2 path the version was still out of date. So I had to download the phar file and point the project to there to work.

Steps to reproduce

Try setting up Drupal CMS with automatic updates on Hostinger

Proposed resolution

Add a UI to allow the path to composer to be configured and link this UI if composer cannot be found or is out-of-date.

Remaining tasks

User interface changes

New UI page to allow package_manager.settings (or parts of it) to be configured

Introduced terminology

API changes

None

Data model changes

None

Release notes snippet