Fix/adding delete billing plan endpoint

[MuthoniMN]

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Description

Creating an endpoint for the delete billing plan controller method
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Related Issue (Link to Github issue)

#641
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Motivation and Context

A delete endpoint will be made available
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How Has This Been Tested?

1. Run the app locally using php artisan serve
2. In Postman, send a DELETE request to /api/v1/billing-plans/{id] with the following:
   Headers:

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

3. You can receive either of these 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: {}
}

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Screenshots (if appropriate - Postman, etc):

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Types of changes

• 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 change)
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Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.