schema propagation util

# Description

To migrate to v2 migrations it will be necessary to get a reflection of the currently deployed schema. We will offer two options.

## Propagate flag

A flag in `_meta` to tell to not execute this migration on the database, but learn the schema from the executed commands.

## Propagate plugin

A plugin adding functionality to execute v1 migrations that have been executed already and learn through the commands executed the schema. It will document failed operations, and stop at failure to let the user intervene by adding a migrate functionality on the failed migration where he can describe the changes made with the new v2 functions.