Set allow-plugins for Composer 2.2

[villfa]

What is the reason for this PR?

A new configuration allow-plugins has been introduced with Composer 2.2: https://github.com/composer/composer/releases/tag/2.2.0-RC1

Quote from Composer's documentation:

Defaults to null (allow all plugins implicitly) for backwards compatibility until July 2022. At that point the default will become {} and plugins will not load anymore unless allowed.

As of Composer 2.2.0, the allow-plugins option adds a layer of security allowing you to restrict which Composer plugins are able to execute code during a Composer run.

When a new plugin is first activated, which is not yet listed in the config option, Composer will print a warning. If you run Composer interactively it will prompt you to decide if you want to execute the plugin or not.

• A new feature
• Fixed an issue (resolve #ID)
• UX improvement

Author's checklist

• Follow the Contribution Guide
• New features and changes are documented

Summary of changes

I've set allow-plugins with the only composer plugin used (bamarni/composer-bin-plugin).

Review checklist

• All checks have passed
• Changes are approved by maintainer

[pimjansen]

How will this run on composer 1?

[villfa]

It will be simply ignored.