Migrate user-attachments images to local repository with relative paths (#184)

* Initial plan

* Migrate user-attachments images to local repository

Co-authored-by: FidelusAleksander <63016446+FidelusAleksander@users.noreply.github.com>

* Update start-exercise workflow to v0.8.1 and checkout main branch

Co-authored-by: FidelusAleksander <63016446+FidelusAleksander@users.noreply.github.com>

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: FidelusAleksander <63016446+FidelusAleksander@users.noreply.github.com>

Author: Copilot