Add error handling and logging to MentionsConverter

Everyone can contribute. Help move this issue forward while earning points, leveling up and collecting rewards.

• Work on this issue
• Close this issue

As suggested in https://gitlab.com/gitlab-com/dev-sub-department/section-dev-request-for-help/-/issues/242#note_1897111619 we should add some error handling in MentionsCoverter so that the import isn't blocked by non-blocking logic.