Relative links to file in repository in Merge Request descriptions does not work
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### Summary
Using a Merge Request template having a relative link reference to a file in the repository creates a non-working link in the Merge Request display.
### Steps to reproduce
<!-- Describe how one can reproduce the issue - this is very important. Please use an ordered list. -->
- Create a file `.gitlab/merge_request_templates/Default.md` with the following content (commit and push to the main branch):
```markdown
Here is a link to the [README](../../README.MD).
```
- Create a new branch, no need for any change, open a new Merge Request
### Example Project
<!-- If possible, please create an example project here on GitLab.com that exhibits the problematic
behavior, and link to it here in the bug report. If you are using an older version of GitLab, this
will also determine whether the bug is fixed in a more recent version. -->
https://gitlab.com/gjourdanweil/test-relative-link-mr-template
Example MR: https://gitlab.com/gjourdanweil/test-relative-link-mr-template/-/merge_requests/2
### What is the current *bug* behavior?
<!-- Describe what actually happens. -->
The link is the Merge Request display goes to `https://gitlab.com/gjourdanweil/test-relative-link-mr-template/-/README.MD` (404).
### What is the expected *correct* behavior?
<!-- Describe what you should see instead. -->
It should go to the file in repository, something like `https://gitlab.com/gjourdanweil/test-relative-link-mr-template/-/blob/main/README.md`
### Relevant logs and/or screenshots
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as it's tough to read otherwise. -->
{width=544 height=600}
### Output of checks
<!-- If you are reporting a bug on GitLab.com, uncomment below -->
This bug happens on GitLab.com (and self hosted as well).
<!-- and uncomment below if you have /label privileges -->
/label ~"reproduced on GitLab.com"
<!-- or follow up with an issue comment of `@gitlab-bot label ~"reproduced on GitLab.com"` if you do not -->
issue