[Settings]: Main Landmark is not defined on the Settings page.

### Windows Terminal version

1.12.3472.0

### Windows build number

10.0.22504.1010

### Other Software

**Test Environment:**
OS: Windows 11 Version Dev (OS Build 22504.1010)
App: Windows Terminal Preview
Screen Reader: Narrator
Tool: Accessibility Insights for Windows Version 1.1.1741.1

### Steps to reproduce

**Repro Steps:**
1. Open Windows Terminal.
2. Open Settings page using 'Ctr+,'.
3. Open Narrator using 'Win+Ctrl+ Enter' key. Turn ON Narrator scan mode using 'Caps lock + Space' key.
4. Now navigate through landmark using shortcut key 'd' or 'Shift + d' and observe the issue.

**User Experience:**
Screen Reader users UX will be not good if landmark is not defined on the page for fast navigation.

**Guideline Reference:**
https://www.w3.org/WAI/WCAG21/Understanding/bypass-blocks

**Attachments:**
[Main Landmark is not defined on the Settings page..zip](https://github.com/microsoft/terminal/files/7750232/Main.Landmark.is.not.defined.on.the.Settings.page.zip)

### Expected Behavior

Main Landmark should be defined on the Settings page so that Screen Reader users can jump from one section/region to another.

### Actual Behavior

Main Landmark is not defined on the Settings page. Only navigation landmark is defined on the page.

No source file or test is named. First reproduce the Settings-page behavior with Narrator or Accessibility Insights and locate the Settings page entry point; done means the page exposes a main landmark in addition to its navigation landmark and the reported keyboard navigation reaches it.

Written by the indexing model from the issue text.