fix: Fix extra-packages CLI parameters to be multi-option

[luanpotter]

This partially solves #12

Before this the extra-packages parameters was misconfigured making it impossible to specify multiple extra packages, and at the same time causing issues on deserialization:

Unhandled exception:
type 'String' is not a subtype of type 'List<String>?' in type cast
#0      getMultiOption (package:ignite_cli/utils.dart:86:29)
#1      createCommand (package:ignite_cli/commands/create_command.dart:54:25)
#2      mainCommand (package:ignite_cli/main.dart:73:11)
<asynchronous suspension>

Now this is fixed; note that if you don't specify --interactive=false it will still be waiting on this step to allow for more selections (but the specified options via arg will be pre-selected instead of the default).

ignite create --name=test --org=org.system32uwu.games --create-folder=true --flame-version=1.8.0 --extra-packages=flame_audio --extra-packages=flame_svg --template=example --interactive=false

[spydon]

Noice!