feat: Add option to generate project using numbers

[pdobrowolski99]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

nestjs/nest-cli#1519

Issue Number: 1519

What is the new behavior?

You can generate project using numbers only.

Does this PR introduce a breaking change?

• Yes
• No

Other information

[micalevisk]

thanks! 😸

Can you test this fix with @nestjs/cli? I mean,

• does the nest new project name's prompt remains the same?
• does the nest new 123 works as expected now?

[pdobrowolski99]

Tested using npm link

[kamilmysliwiec]

LGTM