remove transactions from model-layer "infix" functions

[coeit]

Thanks to @framirez07 it became apparent that adding (or removing) more than 4 associated records in the add<Model> input argument for a to_many association will lead to a Operation Timeout Error.
This is because every associated record starts a transaction in the model-layer "infix" function inside a for await loop in the resolver, which causes the database (or sequelize) to do a Timeout.

To fix this bug remove the transactions from the model-layer infix functions in sql-models and sql-adapter by changing the add_ and remove_ functions as sketched below

NEW "infix" function

static async add_accessionId(measurement_id, accessionId) {
        let updated = await Measurement.update({
                accessionId: accessionId
            }, {
                where: {
                    measurement_id: measurement_id
                }
            })
        return updated;
    }

update respective unit tests

[framirez07]

Done in this commit.