Output file access permissions are unusual

Output file permissions are currently set to `0700` on creation for both files and directories. Typically, files are created as `0644` and directories as `0755`, at least that's the default behavior for most shells on Unix-y systems. Would it be possible to change the way files are created by default, or provide flags to control the behavior?

https://github.com/vmware-tanzu/carvel-ytt/blob/0b8c690e3dc3edeba1e819d13de67ec3c22aa322/pkg/files/output_file.go#L35

https://github.com/vmware-tanzu/carvel-ytt/blob/0b8c690e3dc3edeba1e819d13de67ec3c22aa322/pkg/files/output_file.go#L40

Thanks for the great tool!