Add db_converter

[O2eg]

db_converter is an open-source database migration tool for PostgreSQL 9.6+ designed for high loaded installations.

Tasks that can be solved using db_converter:

• Transactional modification of data of any volume
• Database structure changing with locks control
• System and application notifications via mattermost (or any other messenger)
• Database maintenance (deleting old data, creating new schemas, etc.)
• Export data in csv format into encrypted archive

The key features are:

• Only plain SQL scripts with placeholders
• Parallel processing of several databases
• Handling of the locks to avoid impact on the regular workload

Use cases