Website Markdown cleanup

[tobias-tengler]

Just some small changes that should make the documentation more consistent from a visual standpoint.

• Makes the ExampleTabs known to MDX, so you can just use them without having to import them

• Adds a Warning component that can be rendered by prefixing the markdown message with > Warning:

• Adds a PackageInstallation component that renders (consistent) instructions on how to install the package. Usage: <PackageInstallation packageName="HotChocolate.Data.EnitytFramework" />

• Correctly redirects to 404 page in nginx configuration