Feature/payment

[paulinemwihakimuiruri]

Description

This PR implements the payment app handling mobile money transactions using Safaricom's Daraja API. It provides:

• USSD push payment initiation API with input validation.
• Payment model to track transaction status and details.
• Callback endpoint to receive payment results and update records.

Perhaps answering the following questions will help create a good description:

• What is this?
• Why this?
• How are you doing this?

Figma-[

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ERD-Link
Clickup-Link

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Optimization
• Improvement
• Bug fix

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[emelineniyogisubizo]

Reviewed