docs(auth): update passwordless authentication configuration guide

[ahmedhamouda78]

Description of changes:

Updated documentation to reflect the new passwordless authentication support in defineAuth (implemented in amplify-backend PR #3053).

Changes include:

• Removed warning callout stating passwordless configuration is not available in defineAuth
• Added configuration examples for Email OTP (otpLogin: true on email login)
• Added configuration examples for SMS OTP (otpLogin: true on phone login)
• Added configuration examples for WebAuthn passkeys with automatic and manual relying party ID configuration
• Updated set-up-auth page to mention passwordless as a configuration option
• Updated CDK overrides page to recommend the new defineAuth approach over manual overrides
• Clarified that passwordless methods work alongside password authentication (password auth cannot be disabled)

Related GitHub issue #, if available:

Closes aws-amplify/amplify-backend#2276

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Which product(s) are affected by this PR (if applicable)?

• amplify-cli
• amplify-ui
• amplify-studio
• amplify-hosting
• amplify-libraries

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• JS
• Swift
• Android
• Flutter
• React Native

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