debugger: Update docs with more examples (#31597)

This PR also shows more completion items when defining a debug config in
a `debug.json` file. Mainly when using a pre build task argument.

### Follow ups
- Add docs for Go, JS, PHP
- Add attach docs

Release Notes:

- debugger beta: Show build task completions when editing a debug.json
configuration with a pre build task
- debugger beta: Add Python and Native Code debug config
[examples](https://zed.dev/docs/debugger)

crates/dap_adapters/src/python.rs

@@ -660,7 +660,7 @@ impl DebugAdapter for PythonDebugAdapter {
             }
         }
 
-        self.get_installed_binary(delegate, &config, None, None, false)
+        self.get_installed_binary(delegate, &config, None, toolchain, false)
             .await
     }
 }