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/zed/src/zed.rs

@@ -645,6 +645,7 @@ fn register_actions(
                     files: true,
                     directories: true,
                     multiple: true,
+                    prompt: None,
                 },
                 DirectoryLister::Local(
                     workspace.project().clone(),
@@ -685,6 +686,7 @@ fn register_actions(
                     files: true,
                     directories: true,
                     multiple: true,
+                    prompt: None,
                 },
                 DirectoryLister::Project(workspace.project().clone()),
                 window,