fix: Preview picture not visible on Markdown file (#5781)

Extend API MarkupOptions to contain branch path.

The `api.MarkupOptions{}`  to have `BranchPath` which contains the
current branch. The `RenderMarkup` function utilizes a struct since there
are too many variables passed as arguments and that is not a good sign
for readability.

And `repo-editor.js` will contain a new form data which is `branch-path`
which will then be utilized by `edit.tmpl` as `data-branch-path`.

Closes: #4510

## Checklist

The [contributor guide](https://forgejo.org/docs/next/contributor/) contains information that will be helpful to first time contributors. There also are a few [conditions for merging Pull Requests in Forgejo repositories](https://codeberg.org/forgejo/governance/src/branch/main/PullRequestsAgreement.md). You are also welcome to join the [Forgejo development chatroom](https://matrix.to/#/#forgejo-development:matrix.org).

### Tests

- I added test coverage for Go changes...
  - [ ] in their respective `*_test.go` for unit tests.
  - [ ] in the `tests/integration` directory if it involves interactions with a live Forgejo server.
- I added test coverage for JavaScript changes...
  - [ ] in `web_src/js/*.test.js` if it can be unit tested.
  - [x] in `tests/e2e/*.test.e2e.js` if it requires interactions with a live Forgejo server (see also the [developer guide for JavaScript testing](https://codeberg.org/forgejo/forgejo/src/branch/forgejo/tests/e2e/README.md#end-to-end-tests)).

### Documentation

- [ ] I created a pull request [to the documentation](https://codeberg.org/forgejo/docs) to explain to Forgejo users how to use this change.
- [ ] I did not document these changes and I do not expect someone else to do it.

### Release notes

- [ ] I do not want this change to show in the release notes.
- [x] I want the title to show in the release notes with a link to this pull request.
- [ ] I want the content of the `release-notes/<pull request number>.md` to be be used for the release notes instead of the title.

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/5781
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Co-authored-by: Nirmal Kumar R <tildezero@gmail.com>
Co-committed-by: Nirmal Kumar R <tildezero@gmail.com>

templates/repo/editor/edit.tmpl

@@ -28,7 +28,7 @@
 			<div class="field">
 				<div class="ui top attached tabular menu" data-write="write" data-preview="preview" data-diff="diff">
 					<a class="active item" data-tab="write">{{svg "octicon-code"}} {{if .IsNewFile}}{{ctx.Locale.Tr "repo.editor.new_file"}}{{else}}{{ctx.Locale.Tr "repo.editor.edit_file"}}{{end}}</a>
-					<a class="item" data-tab="preview" data-url="{{.Repository.Link}}/markup" data-context="{{.RepoLink}}/src/{{.BranchNameSubURL}}" data-markup-mode="file">{{svg "octicon-eye"}} {{ctx.Locale.Tr "preview"}}</a>
+					<a class="item" data-tab="preview" data-url="{{.Repository.Link}}/markup" data-context="{{.RepoLink}}" data-branch-path="{{.BranchNameSubURL}}" data-markup-mode="file">{{svg "octicon-eye"}} {{ctx.Locale.Tr "preview"}}</a>
 					{{if not .IsNewFile}}
 					<a class="item" data-tab="diff" hx-params="context,content" hx-vals='{"context":"{{.BranchLink}}"}' hx-include="#edit_area" hx-swap="innerHTML" hx-target=".tab[data-tab='diff']" hx-indicator=".tab[data-tab='diff']" hx-post="{{.RepoLink}}/_preview/{{.BranchName | PathEscapeSegments}}/{{.TreePath | PathEscapeSegments}}">{{svg "octicon-diff"}} {{ctx.Locale.Tr "repo.editor.preview_changes"}}</a>
 					{{end}}

templates/swagger/v1_json.tmpl

@@ -24322,6 +24322,10 @@
       "description": "MarkupOption markup options",
       "type": "object",
       "properties": {
+        "BranchPath": {
+          "description": "The current branch path where the form gets posted\n\nin: body",
+          "type": "string"
+        },
         "Context": {
           "description": "Context to render\n\nin: body",
           "type": "string"