Add the clearBuffer action which is in 1.12

  As in microsoft/terminal#10906

  ### Clear Buffer ([Preview](https://aka.ms/terminal-preview))

  This action can be used to manually clear the Terminal buffer. This is useful for scenarios where you're not sitting at a command-line shell prompt and can't easily run `Clear-Host`/`cls`/`clear`.

  **Command name:** `clearBuffer`

  **Default bindings:**

  ```json
  { "command": { "action": "clearBuffer", "clear": "all" } },
  ```

  #### Actions

  | Name | Necessity | Accepts | Description |
  | ---- | --------- | ------- | ----------- |
  | `clear` | Optional | `"screen"`, `"scrollback"`, `"all"` | What part of the screen to clear. <ul><li>`"screen"`: Clear the terminal viewport content. Leaves the scrollback untouched. Moves the cursor row to the top of the viewport (unmodified).</li><li>`"scrollback"`: Clear the scrollback. Leaves the viewport untouched.</li><li>`"all"` (_default_): Clear the scrollback and the visible viewport. Moves the cursor row to the top of the viewport. </li></ul> |
  | `relative` | Optional | Boolean | If true, then adjust the current opacity by the given `opacity` parameter. If false, set the opacity to exactly that value. |

  > [!IMPORTANT]
  > This feature is only available in [Windows Terminal Preview](https://aka.ms/terminal-preview).

TerminalDocs/customize-settings/actions.md

@@ -986,6 +986,28 @@ This scrolls the screen down to the bottom of the input buffer.
 
 <br />
 
+### Clear Buffer ([Preview](https://aka.ms/terminal-preview))
+
+This action can be used to manually clear the Terminal buffer. This is useful for scenarios where you're not sitting at a command-line shell prompt and can't easily run `Clear-Host`/`cls`/`clear`.
+
+**Command name:** `clearBuffer`
+
+**Default bindings:**
+
+```json
+{ "command": { "action": "clearBuffer", "clear": "all" } },
+```
+
+#### Actions
+
+| Name | Necessity | Accepts | Description |
+| ---- | --------- | ------- | ----------- |
+| `clear` | Optional | `"screen"`, `"scrollback"`, `"all"` | What part of the screen to clear. <ul><li>`"screen"`: Clear the terminal viewport content. Leaves the scrollback untouched. Moves the cursor row to the top of the viewport (unmodified).</li><li>`"scrollback"`: Clear the scrollback. Leaves the viewport untouched.</li><li>`"all"` (_default_): Clear the scrollback and the visible viewport. Moves the cursor row to the top of the viewport. </li></ul> |
+| `relative` | Optional | Boolean | If true, then adjust the current opacity by the given `opacity` parameter. If false, set the opacity to exactly that value. |
+
+> [!IMPORTANT]
+> This feature is only available in [Windows Terminal Preview](https://aka.ms/terminal-preview).
+
 ___
 
 ## Visual adjustment commands