Update List all gift cards endpoint description & endpoints names

[ricardoaerobr]

Types of changes

• [ ] New content (endpoints, descriptions or fields from scratch)
• [X] Improvement (make an endpoint's title or description even better)
• [ ] Spelling and grammar accuracy (self-explanatory)

Changelog

Do not forget to update your changes to our Developer Portal's changelog. Did you create a release note?

• [ ] Yes, I already created a release note about this change.
• [X] No, but I am going to.

PR created to update "List all giftcards" endpoints (Giftcard API & Giftcard Provider Protocol API). PR created to update endpoints names (Giftcard API). EDU-12552

[github-actions[bot]]

Thanks for your contribution. The .json file will be checked now with Spectral.