[Woo POS] Handle network error state for Coupons

[AnirudhBhat]

The goal of this task is to handle case where the internet is not available when merchants try to see the coupons list. The screen should present appropriate error message with an option to retry. I believe it would be similar to what we already have in Products and Variations with change in message.

[dangermattic]

Thanks for reporting! 👍