agent: Rename "open configuration" action to "open settings" (#35329)

"Settings" is the terminology we use in the agent panel, thus having the
action use "configuration" makes it harder for folks to find this either
via the command palette or the keybinding editor UI in case they'd like
to change it.

Release Notes:

- agent: Renamed the "open configuration" action to "open settings" for
better discoverability and consistency

crates/ai_onboarding/src/agent_api_keys_onboarding.rs

@@ -136,10 +136,7 @@ impl RenderOnce for ApiKeysWithoutProviders {
                     .full_width()
                     .style(ButtonStyle::Outlined)
                     .on_click(move |_, window, cx| {
-                        window.dispatch_action(
-                            zed_actions::agent::OpenConfiguration.boxed_clone(),
-                            cx,
-                        );
+                        window.dispatch_action(zed_actions::agent::OpenSettings.boxed_clone(), cx);
                     }),
             )
     }