Introduce Nuxt hooks for client interceptors

[Eschricht]

First of all - thanks for an awesome module!

I thought it'd nice to introduce Nuxt runtime hooks to hook into the fetch client(s) interceptors.

So instead of having to create a custom client, we can utilize Nuxt hooks. Example:

export default defineNuxtPlugin((nuxtApp) => {
  // A global interceptor
  nuxtApp.hook('openFetch:onRequest', (ctx) => {
    console.log('My logging', ctx.request)
  })

  // An interceptor for a particular client
  nuxtApp.hook('openFetch:onRequest:myApi', (ctx) => {
    console.log('My logging', ctx.request)
  })
})

I've created a draft PR which implement this feature. I haven't tested it thoroughly yet, I aim to do that later this week.