get all merchants

[JTaylor28]

The “index” endpoints for merchants should:

• render a JSON representation of all records of the requested resource
• always return an array of data, even if one or zero resources are found
• NOT include dependent data of the resource (eg, if you’re fetching merchants, do not send any data about merchant’s items or invoices)
• follow this pattern: GET /api/v1/

https://backend.turing.edu/module3/projects/rails_engine_lite/requirements#:~:text=Example%20JSON%20response%20for%20the%20Merchant%20resource%3A