Fixing add new custom plugin issue.

[talent-guru]

When I added new custom plugin to mercur template project, I found critical Issue.
When I added new custom plugin using "npx medusa plugin:add custom-plugin", it is added ./apps/backend/node_modules, not ./node_modules.
Because of that, got this error:
"""
Error starting server
error: Cannot find module 'custom-plugin/.medusa/server/src/modules/custom
"""

So I try to install shopify-exporter using "npm install", then I've got white admin dashboard issue.
So tried to move custom plugin modules in ./apps/backend/node_modules to ./node_modules, then I see issue fixed successfully.
I think this is so critical issue in Mercur Project.

Thanks.

[vholik]

We dont support v1 anymore. In case you have the same issue on new Mercur open up a seperate issue https://github.com/mercurjs/mercur/issues