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/go.rs

@@ -463,7 +463,7 @@ impl DebugAdapter for GoDebugAdapter {
         };
 
         Ok(DebugAdapterBinary {
-            command: minidelve_path.to_string_lossy().into_owned(),
+            command: Some(minidelve_path.to_string_lossy().into_owned()),
             arguments,
             cwd: Some(cwd),
             envs: HashMap::default(),