chore: add dedicated GoToSocial auth flow

[ayr-ton]

This implementation addresses the GoToSocial verification issue by creating a dedicated GoToSocial authentication class that avoids the problematic "Unauthorized" error handling while maintaining full OAuth compatibility.

Detailed Solution: Complete separation with dedicated auth class that:

• Only checks nodeinfo endpoint for verification
• No OAuth flow during initial verification
• No "Unauthorized" error handling
• Enables "Authorize" button after successful nodeinfo verification
• Maintains full OAuth compatibility for actual authorization

Discussion:
https://meta.discourse.org/t/activitypub-no-user-agent-sent-with-request-failure-while-creating-client/391245/8

[ayr-ton]

Not so ruby savvy, does someone know a way of doing the same thing without errors.clear? 🥲

[ayr-ton]

@pmusaraj Ready for review, after some accumulated learning the second lap resulted in a better implementation (I think).
Didn't felt okay by just removing the button and decided to verify by checking https://#{domain}/.well-known/nodeinfo instead of booting the OAuth2 flow. Let me know what do you think :-)

[pmusaraj]

Thanks @ayr-ton, I will review shortly. Do you have any test gotosocial instance I can use?

[ayr-ton]

Thanks @ayr-ton, I will review shortly. Do you have any test gotosocial instance I can use?

You can use mine: https://ayr-ton.net

If you need a test user as well send me an email via ayrton at riseup.net so I can create one for you