feat(docs): add custom badge generator

[trueberryless]

🧭 Context

In the last npmx meetup, we were discussing the idea of adding a generator inside the docs for custom badges to simplify the process of getting the Markdown content.

So I played around with the idea a little bit and landed on this implementation, which I find pretty useful.

📚 Description

I moved the custom badges docs to their dedicated page because they are like 50% of the features page and I think since there are many subheadings, it makes sense to be able to see them in the ToC (therefore the dedicated page).

And then I created a little BadgeGenerator.vue which let's the user input the package name and the type of info they wanna have in the badge with a little preview.

Feel free to suggest reverts or further ideas for this improvement.

I also played around a bit with updating the package in the ## Examples section dynamically to what the user currently has typed in the input, but I couldn't figure out a clean way to create the code block like this with a component, which sucks a little bit. Therefore, I dropped this, but if you know how we could do that, feel free to guide me to a possible solution.

Here is a deployment preview of the right page: https://docsnpmxdev-git-fork-trueberryless-feature-docs-cus-74ef86-npmx.vercel.app/guide/badges