Add comment block to all migrated code

[FastLee]

Is there an existing issue for this?

• I have searched the existing issues

Problem statement

Currently code migration doesn't mark the files that were migrated.
Related to #3693

Proposed Solution

Add a comment block or comment to each cell that was migrated.

Additional Context

No response

[JCZuurmond]

Currently code migration doesn't mark the files that were migrated.

Files are indirectly marked as a bak file is created for the migrated files. Note that astroid does not support comments, hence it cannot be used to add comments