add package.json entry point in socket.io package.json

[denis99999]

The kind of change this PR does introduce

• [ ] a bug fix
• [ ] a new feature
• [ ] an update to the documentation
• [ ] a code change that improves performance
• [x] other

Current behavior

For the socket.io package, its entry points don't include the package.json file

New behavior

From now, it is included

Other information (e.g. related issues)

This allows this entry to be required to perform additional checks