Add custom error message parameter for ask() function

[EmadBeltaje]

Hello, so i have been using dcli with my dart CLI apps and i faced this limitation where i can't show my own error message so i figured out, why not to add it, it would be amazing to tell user what went wrong in any way i like, so in this pull request i did that and now we can use ask function this way to show our own custom error message.

String name = ask( 'Enter your name', required: true, validator: Ask.regExp(r'^[a-zA-Z\s_]+$'), // name must be alphabetic customErrorMessage: 'Please enter a valid name!', ); // if input was not alphabetic for ex: 1999 it will show our custom error message // instead of showing default message -> Input does not match: ^[a-zA-Z\s_]+$

• Add new parameter called customErrorMessage to ask function 🚀
• Write test code for the new feature 🧪

[bsutton]

thanks for the contribution!
I add a few comments and requested a few fixes - otherwise I'm happy to merge.

I suspect that you are not using the standard dart indentation.
Can you please reformat with 'dart format'.

[EmadBeltaje]

thank you for the feedback, i made all the needed changes hope now everything is good 😁

[bsutton]

dcli 6.0 has been released with this pr included.

Greatly appreciate your work.