Break down import table
<!--IssueSummary start--> <details> <summary> Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards. </summary> - [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=558888) </details> <!--IssueSummary end--> The import table is 900+ lines of code. It could probably be refactored so the code is easier to understand, while keeping all of the existing functionality. app/assets/javascripts/import_entities/import_groups/components/import_table.vue <!--template sourced from https://gitlab.com/gitlab-org/gitlab/-/blob/master/.gitlab/issue_templates/Default.md-->
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