Enable Kroki diagrams on gitlab.com
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[Kroki support](https://docs.gitlab.com/ee/administration/integration/kroki.html#kroki-diagrams) has been added and available in the product since %13.7.
However it's not enabled in gitlab.com proper. To do so requires some work by infrastructure to run our own instance of the Kroki server. That issue is https://gitlab.com/gitlab-com/gl-infra/infrastructure/-/issues/12026
A relevant discussion on that issue is https://gitlab.com/gitlab-com/gl-infra/reliability/-/issues/12026#note_876520955.
This issue is for tracking the infrastructure issue, as well as any additional discussion that might be needed.
Please note that this follows from https://gitlab.com/gitlab-org/gitlab/-/issues/241744+, which has 35 upvotes.
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