GitLab Migration: Improve text on PAT usage

What does this MR do and why?

This MR introduces the following text changes for GitLab migration:

• Adds the required scope (api and read_repository) to the personal access token information.
• Changes the wording and advise users to consider an expiration date according to the size of the migration

Screenshots or screen recordings

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #384324 (closed)