feat: use nuxt-site-config module if available for origin extraction

[astraldev]

Fixes #500

I've added an extra plugin to check if nuxt site config is available, and use it's getNitroOrigin composable at the getOAuthRedirectURL method

[atinux]

Not sure I am happy with this approach, most people use the NUXT_PUBLIC_SITE_URL env variable, worst case we can read from it

[astraldev]

Understandable, if the module itself can have support for a base url, then there would be no need for it. I picked it since the getNitroOrigin is a well feature packed utility.

Would you prefer I clone it instead (only the relevant part)? So we don't rely on that?

It's quite strange, we have to configure the redirect url for each oauth provider manually.

Using the NUXT_SITE_PUBLIC_URL would still mean having to manually configure each of them again since the guess method doesn't really do so well

[atinux]

But my main concern is why the current behavior does not work for you @astraldev?