fix: init to support non-empty directories

[tomfrew]

Previous behaviour

• When running keel init in a non-empty directory it would just error and exit
• This included an "empty" directory that had just been git initialised (i.e. contained a .git directory)

New behaviour

• keel init will run in non-empty directories but will not overwrite any existing files
• The command output shows which files have been generated and while have been skipped due to existing files

Note

This is a quick fix to improve the DX of this command. An overhaul of the keel init command is coming soon

[davenewza]

I need this feature like every single time I start a new Keel app 👏