Add option for enabling SVG support for PlantUML
<!--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=434357) </details> <!--IssueSummary end--> <!-- This template is a great use for issues that are feature::additions or technical tasks for larger issues.--> ### Proposal Due to this [security vulnerability](https://gitlab.com/gitlab-org/gitlab/-/issues/416902) SVG support was removed for PlantUML. However, some customers were using SVG images with PlantUML. We should create a feature flag that would allow customers to re-enable SVG support. Copying message from @robotmay_gitlab in [slack](https://gitlab.slack.com/archives/CK75EF2A2/p1701862931234419): > On .com yeah it won't be coming back I suspect. It would be possible to bring it back for self-hosted but it would require reconfiguring their servers to ensure PlantUML isn't being served from a subfolder on the main GitLab domain, and we'd need to add a feature toggle for it I think <!-- Use this section to explain the feature and how it will work. It can be helpful to add technical details, design proposals, and links to related epics or issues. --> <!-- Consider adding related issues and epics to this issue. You can also reference the Feature Proposal Template (https://gitlab.com/gitlab-org/gitlab/-/blob/master/.gitlab/issue_templates/Feature%20proposal%20-%20detailed.md) for additional details to consider adding to this issue. Additionally, as a data oriented organization, when your feature exits planning breakdown, consider adding the `What does success look like, and how can we measure that?` section. --> <!-- Label reminders Use the following resources to find the appropriate labels: - Use only one tier label choosing the lowest tier this is intended for - https://gitlab.com/gitlab-org/gitlab/-/labels - https://about.gitlab.com/handbook/product/categories/features/ -->
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