[Woo POS] Coupons: Handle coupons enabled/disabled in core

[iamgabrielma]

Coupons disabled (WooCommerce > Settings > General > Enable coupons):
Show a message and CTA to enable coupon functionality. Reload the list once the setting is enabled.

Ref: pdfdoF-6BG-p2#comment-7714

This is handled along with all the other Woo settings. On Android, we fetch them on login
Such settings are not expected to change often.

[dangermattic]

🚫 Please add a type label (e.g. type: enhancement) and a feature label (e.g. feature: stats) to this issue.