Add a command to generate new rules

[GeniJaho]

Why

It's very difficult to add new rules to the repository, every time you have to copy an existing one and change everything.

I think we should implement a way to generate the base scaffolding needed for writing a new rule.

Modifying the CustomRuleCommand in the core Rector repository would make it unnecessarily complicated (rectorphp/rector-src#6676).

Changes

• Ported an implementation of the original command without all the options and dependencies. The reason is I couldn't make RectorConfig run user-defined commands. I think they need to be configured in the core Rector implementation somehow.
• Added a new directory called Commands, registered in autoload-dev so it doesn't make it to the users' vendor.
• Added a new composer script to make it easy to run the command, called composer make:rule.
• Added two new dev dependencies to work with the filesystem, but they can be refactored out since the use-case is very limited.
• To Do: cleanup, remove dependencies, generate configurable rules, add to Readme, etc

@peterfox what do you think? Can we use something like this? Is there a better way to generate new rules?