gpui: Add support for custom prompt text in PathPromptOptions (#36410)

This will be used to improve the clarity of the git clone UI

### MacOS
<img width="1322" height="128" alt="image"
src="https://github.com/user-attachments/assets/3e511143-12c1-4440-89dd-841b21b2e98e"
/>

### Windows 
<img width="338" height="80" alt="image"
src="https://github.com/user-attachments/assets/766d08d6-0c72-4175-ad24-59dc6188d5f1"
/>

### Linux

<img width="387" height="72" alt="Screenshot From 2025-08-18 15-32-06"
src="https://github.com/user-attachments/assets/3125a7c4-3975-462a-a547-d5d4fac48f22"
/>



Release Notes:

- N/A

crates/workspace/src/workspace.rs

@@ -561,6 +561,7 @@ pub fn init(app_state: Arc<AppState>, cx: &mut App) {
                         files: true,
                         directories: true,
                         multiple: true,
+                        prompt: None,
                     },
                     cx,
                 );
@@ -578,6 +579,7 @@ pub fn init(app_state: Arc<AppState>, cx: &mut App) {
                         files: true,
                         directories,
                         multiple: true,
+                        prompt: None,
                     },
                     cx,
                 );
@@ -2655,6 +2657,7 @@ impl Workspace {
                 files: false,
                 directories: true,
                 multiple: true,
+                prompt: None,
             },
             DirectoryLister::Project(self.project.clone()),
             window,