Update an Item

[JTaylor28]

This endpoint should:

• update the corresponding Item (if found) with whichever details are provided by the user
• render a JSON representation of the updated record.
• follow this pattern: PATCH /api/v1/items/:id
• accept the following JSON body with one or more of the following fields: The body should follow this pattern:
  https://backend.turing.edu/module3/projects/rails_engine_lite/requirements#:~:text=%22name%22%3A%20%22value1%22%2C%0A%20%20%22description%22%3A%20%22value2%22%2C%0A%20%20%22unit_price%22%3A%20100.99%2C%0A%20%20%22merchant_id%22%3A%207