feat: add instagram provider

[sandros94]

Adding Instagram as new provider.

To test the provider

1. signup to https://developers.facebook.com
2. create a new app at https://developers.facebook.com/apps
3. while creating the app, at Use Cases, pick Other (last option)
4. once created, in the Dashboard, scroll down to Add products to your app and click set up for Instagram Basic Display
5. once at Basic display, you'll see the Instagram App ID and Secret to use as the provider. Alongside, in this page, you'll find:
   • Valid OAuth Redirect URIs: I've used Cloudflare's tunnel to quickly test this with https
   • Deauthorize callback URL and Data Deletion Request URL: just set the domain for now
   • User Token Generator: this is important, since you need to invite yourself (or someone else) as the test user

Add a test user:

1. Under User Token Generator click on Add or Remove Instagram Testers
2. then click Add People button in the top right
3. select Instagram Tester at the bottom of that modal and search for the username to add
4. open Instagram's Apps and Websites setting page (if you are still on the app user's list there is a convenient link to click
   
5. go to the Tester Invites (all the way to the right) and accept it
6. test the login
   

[atinux]

Thank you!