Follow Up to supporting attachment import from GHE Server
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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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