Improve config diff logic

[viktorprogger]

In my opinion we can fully remove dist directories/files from a project instead of #42. Not just remove, but replace with another functionality.

I see 6 use-cases to activate this package as a composer plugin:

1. composer install when composer.lock exists
2. composer install when composer.lock does not exist
3. composer update
4. composer require an existing package, but in another version
5. composer require a new package
6. composer require yiisoft/config

• In case 1 this package should do nothing. All the packages had been installed earlier, and their configs - too.
• Cases 2-4 looks similar for me: it's about package(s) updating. In this case the config package should provide the choice for a user (read below about it).
• In the cases 5 and 6 the config package should copy all the configurations from the vendor directory (for a single package in case 5 and for all the packages in case 6), and ask a user what to do when a file with the required name exists in a project.

Let's talk about the logic when the plugin sees some differences

When there are some differences, the plugin should ask a user what to do. All available variants are:

• Show diff between a local (in -project) version and a new version (in the vendor directory after package updating/requiring).
• Show diff between an old version (copied before package update) and a new version
• Replace local version with a new version (default when there was no local version)
• Copy a new version to a project with different name. This file shouldn't be included to the merge plan
• Ignore, do nothing (default when there is a local config version)
• 3 previous variants, but "For all" (ignore/copy/replace for this and all the future questions)

When a composer command is executed in a non-interactive mode, then the config package should automatically choose the default variant.

[samdark]

Seems to be entirely possible with PRE_PACKAGE_INSTALL and PRE_PACKAGE_UPDATE that are executed before new files are fetched into vendor. This way we can get config we're updating from and, indeed, we don't need dist in this case.

[samdark]

Interactive IO is possible as well with:

/** @var IOInterface $io */
$io->ask('bla-bla');

[samdark]

As an additional option config asks we can have an option to skip copying default config (or all default configs). That will be useful for having totally custom configs that aren't related to what's in the packages.