Include link to raw job log in plain-text emails

What does this MR do?

People who prefer plain text email also might prefer the raw job log files. So include the link directly to there.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/56849

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content