feat: backend functions for buy giftcard

[Syn-McJ]

Issue being fixed or feature implemented

• We need to implement buying the gift card

What was done?

• API requests for getting payment URL
• BIP70 calls for payment
• Additional UI
• Token refresh logic
• Min/max limit error processing

How Has This Been Tested?

QA

Breaking Changes

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated relevant unit/integration/functional/e2e tests
• I have made corresponding changes to the documentation

For repository code-owners and collaborators only

• I have assigned this pull request to a milestone

[pankcuf]

LGTM