feat: add is_anonymous claim to Auth hook jsonschema (supabase#1667)

## What kind of change does this PR introduce?

Add is_anonymous claim to hook spec to ensure that generated tokens
always contain the is_anonymous claim.

internal/hooks/auth_hooks.go

@@ -93,7 +93,7 @@ const MinimumViableTokenSchema = `{
       "type": "string"
     }
   },
-  "required": ["aud", "exp", "iat", "sub", "email", "phone", "role", "aal", "session_id"]
+  "required": ["aud", "exp", "iat", "sub", "email", "phone", "role", "aal", "session_id", "is_anonymous"]
 }`
 
 // AccessTokenClaims is a struct thats used for JWT claims