Specify Webpack >=5.0.0 as peer dependency

[lg-kialo]

Is your feature request related to a problem? Please describe.
The README says that starting with version 6, the plugin only works with Webpack 5+.
But this is not reflected in the peerDependencies of the package.json so when updating my project's dependency this requirement is ignored.

Describe the solution you'd like
Add a peerDependencies section in the package.json specifying that the plugin works with Webpack 5+.
Like this:

{
    ...
    "peerDependencies": {
        "webpack": ">=5.0.0"
    }
}

Describe alternatives you've considered
The alternative is that developers who use your package need to pay attention to the note in the README about compatibility with Webpack, I guess.

Additional context
No additional context.

[ztoben]

Missed this when doing the original major update to webpack 5, so I've pushed this in version 7.0.0 in case there are backward compatibility issues surfaced by the change. Thanks!