chore: 🔧 improve contributing by setting up a monorepo

Hey there!

Really appreciate your work on `enhance-custom-element`. For me it feels a bit hard to contribute and to get together how all parts work together, as everything is distributed in different repositories which is very hard to follow as an outstander.

Do you see a chance on setting up the following repos as a monorepo?

- "@enhance/element"
- "@enhance/base-element"
- "@enhance/custom-element-mixin"
- "@enhance/event-handler-mixin"
- "@enhance/morphdom-mixin"
- "@enhance/shadow-element-mixin"
- "@enhance/template-mixin"

I'm open to contribute on this issue especially if you're fine with using `pnpm`, which has first-class workspace support and handles versioning etc. very well. If you want to stick to `npm` I would have to jump into their monorepo config, which I'm not used to, but I could wrap my head around it – would just take longer. (Usually working with semantic-release and semantic-release-monorepo, but I think you're release pipeline could be integrated in a monorepo setup as well.)