fix(demo): Fixes webpack serve/demo to 5.x compatible

[ellinge]

Changes to webpack-dev-server which is compatible with webpack 5.x, adds missing typescript definition for property

What does it do?

Had issues getting development going since the project uses webpack 5.x but webpack-serve depends on 4.x.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• Updated documentation (if applicable)
• Added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• My changes generate no new warnings

[github-actions]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed in 10 days if no further activity occurs. Thank you for your contributions.