Add "Include development modules?" checkbox on Create Platform form

This is essentially a front-end subset of the functionality provided by #3067154: Add property to platforms "composer_install_command" to allow each platform to decide what composer install options to use., to determine whether or not users want to include development modules in their platform.

By default, we get this:

composer install --no-interaction --no-progress --no-dev

However, on Dev environments, the following would be more helpful:

composer install --no-interaction --no-progress

This would allow (for example) the Devel module to be included in the platform, which you would want on Dev, but not on Prod (the default).

So let's add a checkbox on the Create Platform form that allows for this option on the front-end:

• Include development modules?

Help text can be something like,

If you're using Composer to build sites, and you'd like to include the development modules listed in the require-dev section of composer.json (e.g. Devel), check this box. This will have no effect on non-Composer-based sites.