Fix: missing route for controller method

[MuthoniMN]

Description

The "destroy" method in BillingPlanController doesn't have a route, documentation or related tests

Acceptance Criteria

• DELETE endpoint (/api/v1/billing-plans/{id})
• Documentation for the endpoint
• Test cases

Request

DELETE - /api/v1/billing-plans/{{plan_id}}

{
     Authorization: "Bearer {auth-token}"
}

Responses

204 - Successful deletion

{
  status: "error",
  status_code: 204
  message: "This billing plan was successfully deleted",
  data: {}
}

404 - Billing plan not found

{
  status: "error",
  status_code: 404
  message: "This billing plan not found",
  data: {}
}

500 - Internal Server Error

{
  status: "error",
  status_code: 500,
  message: "Internal server error",
  data: {}
}