Add CLI command to migrate imports to @openedx scope

[viktorrusakov]

As of v21.5.7 we started publishing Paragon under @openedx scope instead of @edx, meaning that all consuming applications that decide to upgrade to this version or above will have to migrate all of their imports of Paragon to @openedx/paragon. Instead of having them do it manually, we should create a CLI command that will ease the migration process.

• Add a migrate-to-openedx-scope CLI command to paragon-cli that scans all files in consuming applications and makes following replacement: @edx/paragon --> @openedx/paragon. This should be applied to all files (not just .jsx, but .md, .scss etc.)