debugger: Mark DebugAdapterBinary::program as optional (#32534)

This allows us to support debugging with a debug adapter not managed by
Zed. Note that this is not a user facing change, as DebugAdapterBinary
is used to determine how to spawn a debugger. Thus, this should not
break any configs or anything like that.

Closes #ISSUE

Release Notes:

- N/A

crates/dap_adapters/src/codelldb.rs

@@ -359,7 +359,7 @@ impl DebugAdapter for CodeLldbDebugAdapter {
         };
 
         Ok(DebugAdapterBinary {
-            command: command.unwrap(),
+            command: Some(command.unwrap()),
             cwd: Some(delegate.worktree_root_path().to_path_buf()),
             arguments: vec![
                 "--settings".into(),