Accessibility: Add label to plugin checkboxes on settings modal

[sejas]

• Closes https://github.com/WordPress/wordpress-playground/issues/617

Description

It re-uses the already existing text as a label for plugin checkboxes on the settings modal

Testing instructions

• In a terminal run:
  • yarn install
  • composer install
  • yarn wp-env start # to start the main server
• In a new terminal run:
  • cd source/wp-content/themes/wporg-wasm/src/wasm-demo
  • nvm use v14.21.3
  • yarn install
  • yarn start # to start the wasm demo block
• Go to /wp-admin
• Activate the theme Wasm if it's not active yet.
• Create a new page
• Embed the block wasm demo
• View the forntend page
• Click on the settings button to open the modal
• Inspect the checkboxes
• Observe there is a new label element wrapping the checkbox items.
• Run axe chrome extension
• Observe there are seven less errors.

Screenshot

Before

After