UX: adds chat send shortcut user preference (#30473)

Users can now decide if they want to send a message on:
- <kbd>enter</kbd>
- <kbd>meta + enter</kbd>

If you choose <kbd>meta + enter</kbd>, <kbd>enter</kbd> will add a
linebreak.

<img width="192" alt="Screenshot 2025-01-21 at 12 57 48"
src="https://github.com/user-attachments/assets/abfd6f8b-83b3-4e6f-be67-8f63d536ca8a"
/>

plugins/chat/spec/system/chat_composer_spec.rb

@@ -104,6 +104,74 @@ RSpec.describe "Chat composer", type: :system do
 
       expect(channel_page.composer.value).to eq("bb")
     end
+
+    context "when user preference is set to send on enter" do
+      before { current_user.user_option.update!(chat_send_shortcut: 0) }
+
+      context "when pressing enter" do
+        it "sends the message" do
+          chat_page.visit_channel(channel_1)
+
+          channel_page.composer.fill_in(with: "testenter").enter_shortcut
+
+          expect(channel_page.messages).to have_message(text: "testenter")
+        end
+      end
+
+      context "when pressing shift + enter" do
+        it "adds a linebreak" do
+          chat_page.visit_channel(channel_1)
+
+          channel_page.composer.fill_in(with: "testenter").shift_enter_shortcut
+
+          expect(channel_page.composer.value).to eq("testenter\n")
+        end
+      end
+
+      context "when pressing meta + enter" do
+        it "sends the message" do
+          chat_page.visit_channel(channel_1)
+
+          channel_page.composer.fill_in(with: "testenter").meta_enter_shortcut
+
+          expect(channel_page.messages).to have_message(text: "testenter")
+        end
+      end
+    end
+
+    context "when user preference is set to send on meta + enter" do
+      before { current_user.user_option.update!(chat_send_shortcut: 1) }
+
+      context "when pressing enter" do
+        it "adds a linebreak" do
+          chat_page.visit_channel(channel_1)
+
+          channel_page.composer.fill_in(with: "testenter").enter_shortcut
+
+          expect(channel_page.composer.value).to eq("testenter\n")
+        end
+      end
+
+      context "when pressing shift + enter" do
+        it "adds a linebreak" do
+          chat_page.visit_channel(channel_1)
+
+          channel_page.composer.fill_in(with: "testenter").shift_enter_shortcut
+
+          expect(channel_page.composer.value).to eq("testenter\n")
+        end
+      end
+
+      context "when pressing meta + enter" do
+        it "sends the message" do
+          chat_page.visit_channel(channel_1)
+
+          channel_page.composer.fill_in(with: "testenter").meta_enter_shortcut
+
+          expect(channel_page.messages).to have_message(text: "testenter")
+        end
+      end
+    end
   end
 
   context "when editing a message with no length" do