Migrate existing instance integrations from intergrations to instance_integrations table

As part of &14638 we need to migarate existing instance wide integrations that are located in integrations table to a new instance_integrations table, so that once we switch to using InstanceIntegration model, we have all the 'old' integrations present in the new table.

Proposed solution

1. Create a background data migration that copies instance wide integrations (instance: true & group/project foreign key is null) from integrations to instance_integrations table while preserving all values