Allow updating of attendee capabilities in the demo

[simmkyu]

Issue #:
N/A

Description of changes:

• Configure attendee abilities on the home screen.
• Adjust attendee capabilities during the session.

Testing:

• N/A as the PR includes only demo changes.

Can these tested using a demo application? Please provide reproducible step-by-step instructions.

See the Test Steps section.

Checklist:

1. Have you successfully run npm run build:release locally?
   N/A

2. Do you add, modify, or delete public API definitions? If yes, has that been reviewed and approved?
   N/A

3. Do you change the wire protocol, e.g. the request method? If yes, has that been reviewed and approved?
   N/A

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

Test Steps

Configuring attendee abilities on the home screen

This section uses the create-attendee API in the server application.

1. Open the Chime SDK Serverless Demo.
2. Select the Additional Options.
3. Update the values for Audio Capability, Video Capability, and Content Capability.
4. Click on the Save button and join a Chime SDK meeting.
5. Ensure that an attendee has specific capabilities.

Updating one attendee's capabilities during the session

This section uses the update-attendee-capabilities API in the server application.
https://awscli.amazonaws.com/v2/documentation/api/latest/reference/chime-sdk-meetings/update-attendee-capabilities.html

1. Open the Chime SDK Serverless Demo.
2. Select the Additional Options.
3. Check the Allow updating of attendee capabilities after start box.
4. Click on the Save button and join a Chime SDK meeting.
5. Confirm that the checkbox appears in the roster.
6. Choose an attendee by checking the box next to their name.
7. Click on the menu located at the top-right corner of the roster.
   
8. Select the Update the selected attendee option.
9. Ensure that the Attendee capabilities window appears, displaying the currently selected attendee's capabilities.
10. Edit the attendee capabilities and click on the Save button.
11. Confirm that the attendee has the specific capabilities. (See the update-attendee-capabilities API documentation for expected behaviors.)

Updating attendee's capabilities, excluding selected attendees, during the session

This section uses the batch-update-attendee-capabilities-except API in the server application.
https://awscli.amazonaws.com/v2/documentation/api/latest/reference/chime-sdk-meetings/batch-update-attendee-capabilities-except.html

1. Open the Chime SDK Serverless Demo.
2. Select the Additional Options.
3. Check the Allow updating of attendee capabilities after start box.
4. Click on the Save button and join a Chime SDK meeting.
5. Confirm that the checkbox appears in the roster.
6. Choose an attendee by checking the box next to their name.
7. Click on the menu located at the top-right corner of the roster.
   
8. Select the Update all attendees, except 1 selected option.
9. The Attendee capabilities window appears with SendReceive set as the default value.
10. Edit the attendee capabilities and click on the Save button.
11. Confirm that all attendees, excluding the selected attendees, have the specific capabilities. (See the batch-update-attendee-capabilities-except API documentation for expected behaviors.)

[xuesichao]

We should refactor our server and handler to node express based so it's easier to maintain.