Embedded snippets: Allow use in GitLab comments

Description

We have a great new community contribution with our "Embedded snippets" feature, available with 10.8.
This feature has potential to be very useful within GitLab comments as well. Right now, script tags are suppressed for security reasons.

<script src="https://gitlab.com/akaemmerle/example-project/snippets/1718255.js"></script>

Proposal

Let's find a way to make this work within GitLab comments.

Links / references

https://gitlab.com/gitlab-org/gitlab-ce/issues/8088