feat: have both local and global interceptors

[enkot]

🔗 Linked issue

#319

❓ Type of change

• 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

Currently interceptors specified in $fetch() override the interceptors in $fetch.create.

This PR adds support for interceptors as an array, so we can merge arrays from $fetch and $fetch.create.
It also allows set an enforce option, so that interceptors from $fetch and $fetch.create can be enforced to append or prepend to the resulting array of interceptors (similar to Nuxt plugins):

const $myFetch = $fetch.create({
  onRequest: [
    (ctx) => { /* Handler 1 */ }, // same as "enforce: 'default'"
    {
      enforce: 'post',
      handler: (ctx) => { /* Handler 2 */ }
    }
  ]
})

$myFetch({
  onRequest: [
    // Will be appended 
    (ctx) => { /* Handler 3 */ },
    // If you need to prepend in some scenarios
    {
      enforce: 'pre',
      handler: (ctx) => { /* Handler 4 */ }
    }
  ]
})

// Interceptors will be executed in this order:
/*
Handler 4
Handler 1
Handler 3
Handler 2
*/

Note

This is implemented as a braking change, but we can add the overrideInterceptors option to not break the current behavior.

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.