.gitlab/issue_templates: Move suggestions into comments

.gitlab/issue_templates: Move suggestions into comments

Many users forget to remove the suggestions from the bug template
when creating a new issue. So when searching for strings like "s390x"
or "Windows", you get a lot of unrelated issues in the results.
Thus let's move the suggestions into HTML comments - so they will
still show up in the markdown when editing the bug, while being
hidden/ignored in the final text or in the search queries.

Message-Id: <20221201133756.77216-1-thuth@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>