Follow Up to supporting attachment import from GHE Server
<!--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> - [Work on this issue](https://contributors.gitlab.com/manage-issue?action=work&projectId=278964&issueIid=562140) </details> <!--IssueSummary end--> A few follow-up tasks from https://gitlab.com/gitlab-org/gitlab/-/merge_requests/197673+ need to be done: - Do not update file/image attachment URLs in code/DiffNotes (see https://gitlab.com/gitlab-org/gitlab/-/merge_requests/197673#note_2690596694+) - update description in specs. (see https://gitlab.com/gitlab-org/gitlab/-/merge_requests/197673#note_2690354663+ https://gitlab.com/gitlab-org/gitlab/-/merge_requests/197673#note_2690355179+ - fix rubocop offence and throw an error (see https://gitlab.com/gitlab-org/gitlab/-/merge_requests/197673#note_2690596662+) - add method `enterprise_import?` on client class (see https://gitlab.com/gitlab-org/gitlab/-/merge_requests/197673#note_2690596667+) - update comment to include client arg (see https://gitlab.com/gitlab-org/gitlab/-/merge_requests/197673#note_2690596673+ and https://gitlab.com/gitlab-org/gitlab/-/merge_requests/197673#note_2690596680+) - always initialize a MarkdownText object (see https://gitlab.com/gitlab-org/gitlab/-/merge_requests/197673#note_2690596681+ and https://gitlab.com/gitlab-org/gitlab/-/merge_requests/197673#note_2690596683+) - move web_endpoint sanitizing logic to client (see https://gitlab.com/gitlab-org/gitlab/-/merge_requests/197673#note_2690596678+)
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