Improve migration script

[Neylix]

Description

This PR makes the migration script running asynchronously. It prevent the erlang upgrade process to wait for the end of migration that can take a while.

Also improve the max_concurrency option in async_stream process to speed up the migration task

Redirect migration script folder to prod when running a release from dev en

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules