feat: allow providing current directory in init command

[szymonrybczak]

Summary:

Context: #365 (comment).

Test Plan:

1. Clone the repository and do all the required steps from the Contributing guide
2. Run this command:

node /path/to/react-native-cli/packages/cli/build/bin.js init asdf --directory ./

3. Should create project in current directory, if it contains some files it should ask what to do before.

Checklist

• Documentation is up to date to reflect these changes.
• Follows commit message convention described in CONTRIBUTING.md