[BUG] Default sequelize schema ids conflict with primary keys

[Michael-Vol]

Describe the bug
Currently, the sequelize schema adds a default uuid (_id) as a primary key to the model. In case the user provides a database for introspection and the tables have already a primary key, there will be a conflict between that primary key and the _id we are trying to add to the schema.
We need to keep both ids though, since Conduit uses the _id for any queries related to that model.
One possible solution would be to change the _id from primary key to virtual, however sequelize currently doesn't support converting the virtual datatype into the sql equivalent (see sequelize/sequelize#12451).

To Reproduce

1. Start the database module with an existing database connection in the envs
2. Notice that the database won't sync because of the virtual field is not defined.

Expected Behavior
The database module should introspect the db by keeping both it's already defined primary key and adding the conduit _id used for future queries.