feat: added update mode price api for instructors

[AhtishamShahid]

Description

Issue: #37465

This PR adds a new PATCH API endpoint to allow an instructor to update the price for a specific course enrollment mode (e.g., verified).

PATCH /api/instructor/v1/courses/{course_key}/modes/{mode_slug}/price

This endpoint requires InstructorPermission (is_staff) and expects the Content-Type header to be application/merge-patch+json. The price should be sent as an integer in the smallest currency unit (e.g., cents).

Example Request

PATCH /api/instructor/v1/courses/course-v1:TestOrg+CS101+2025/modes/verified/price
Content-Type: application/merge-patch+json
Accept: application/json
X-CSRFToken: [Your-Token-Here]

{
    "price": 3900
}

Success Response

The endpoint returns an empty body with a 204 No Content status upon a successful price update.

HTTP 204 No Content
Allow: PATCH, HEAD, OPTIONS

Error Responses

• 400 Bad Request: If the price field is missing, not an integer, or negative.
• 401 Unauthorized: If the user is not authenticated.
• 403 Forbidden: If the user is not an instructor (is_staff=False).
• 404 Not Found: If the course_key or mode_slug does not exist.
• 415 Unsupported Media Type: If the Content-Type is not application/merge-patch+json.

Testing

• Added new unit tests in lms/djangoapps/instructor/tests/test_api.py under the TestCourseModePriceView class.
• Tests cover success (204), auth (401), permissions (403), not found (404), and various bad request (400) scenarios.

[Copilot]

Pull Request Overview

This PR adds a new API endpoint for updating the price of a specific course enrollment mode via PATCH request. The endpoint allows instructors and staff to modify course mode pricing dynamically.

• Introduces CourseModePriceView API view with PATCH method for updating mode prices
• Adds ModePriceUpdateSerializer to validate price update requests
• Enhances InstructorPermission to include GlobalStaff user support
• Adds comprehensive test coverage for authentication, authorization, and validation scenarios

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 9 comments.

Show a summary per file

File	Description
lms/djangoapps/instructor/views/serializer.py	Adds ModePriceUpdateSerializer to validate price field in update requests
lms/djangoapps/instructor/views/api_urls.py	Registers new course_mode_price URL pattern for the price update endpoint
lms/djangoapps/instructor/views/api.py	Implements CourseModePriceView with PATCH method and adds import; includes minor typo fix in unrelated docstring
lms/djangoapps/instructor/tests/test_api.py	Adds TestCourseModePriceView test suite covering success, permission, validation, and error cases
lms/djangoapps/instructor/permissions.py	Extends InstructorPermission.has_permission to grant access to GlobalStaff users

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