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>

tests/e2e/markdown-editor.test.e2e.ts

@@ -11,6 +11,37 @@ test.beforeAll(async ({browser}, workerInfo) => {
   await login_user(browser, workerInfo, 'user2');
 });
 
+test('Markdown image preview behaviour', async ({browser}, workerInfo) => {
+  test.skip(workerInfo.project.name === 'Mobile Safari', 'Flaky behaviour on mobile safari;');
+
+  const context = await load_logged_in_context(browser, workerInfo, 'user2');
+
+  // Editing the root README.md file for image preview
+  const editPath = '/user2/repo1/src/branch/master/README.md';
+
+  const page = await context.newPage();
+  const response = await page.goto(editPath, {waitUntil: 'domcontentloaded'});
+  expect(response?.status()).toBe(200);
+
+  // Click 'Edit file' tab
+  await page.locator('[data-tooltip-content="Edit file"]').click();
+
+  // This yields the monaco editor
+  const editor = page.getByRole('presentation').nth(0);
+  await editor.click();
+  // Clear all the content
+  await page.keyboard.press('ControlOrMeta+KeyA');
+  // Add the image
+  await page.keyboard.type('![Logo of Forgejo](./assets/logo.svg "Logo of Forgejo")');
+
+  // Click 'Preview' tab
+  await page.locator('a[data-tab="preview"]').click();
+
+  // Check for the image preview via the expected attribute
+  const preview = page.locator('div[data-tab="preview"] p[dir="auto"] a');
+  await expect(preview).toHaveAttribute('href', 'http://localhost:3003/user2/repo1/media/branch/master/assets/logo.svg');
+});
+
 test('markdown indentation', async ({browser}, workerInfo) => {
   const context = await load_logged_in_context(browser, workerInfo, 'user2');