Swift: Create an anonymous user
- Returns an anonymous user
 
- It is recommended to set up captcha for anonymous sign-ins to prevent abuse. You can pass in the captcha token in the 
options param. 
Examples
Create an anonymous user
let session = try await supabase.auth.signInAnonymously(captchaToken: captchaToken)
Create an anonymous user with custom user metadata
let session = try await supabase.auth.signInAnonymously(
  data: customData,
  captchaToken: captchaToken
)