Drop GFM support for the title of Milestone/MergeRequest in template

Description

The title of Milestone/MergeRequest should be treated as plain, not as markdown (GFM), when linking the title to the Milestone/MergeRequest with link_to_gfm as seen #34289 (closed).

Proposal

Use link_to instead of link_to_gfm in their templates. link_to is much faster than link_to_gdm.

Note

The title/full_title of Commit is expected to be in the markdown format so this proposal leaves it as is.

Links / references

#34289 (closed)

/label ~"feature proposal" milestones backend ~performance