This PR introduces the `ReviewedOn` and `ReviewedBy` variables for the
default merge message templates (e.g.,
`.gitea/default_merge_message/MERGE_TEMPLATE.md`).
This allows customizing the default merge messages while retaining these
trailers.
This also moves the associated logic out of `pull.tmpl` into the
relevant Go function.
This is a first contribution towards #11077.
---
For illustration, this allows to recreate the "default default" merge
message with the following template:
```
.gitea/default_merge_message/MERGE_TEMPLATE.md
Merge pull request '${PullRequestTitle}' (${PullRequestReference}) from ${HeadBranch} into ${BaseBranch}
${ReviewedOn}
${ReviewedBy}
```
(cherry picked from commit da4bbc42477ba04d175cc0775a0c5ec90c4c24fe)
Conflicts:
docs/content/usage/merge-message-templates.en-us.md
not in Forgejo
templates/repo/issue/view_content/pull.tmpl
trivial context conflict
4ddd9af50f