feat: Add ANONADDY_PROXY_AUTHENTICATION_SYNC_EMAIL configuration option - #916

This pull request introduces a new configuration option, ANONADDY_PROXY_AUTHENTICATION_SYNC_EMAIL (defaulting to true), which controls whether a user's default recipient email address in AnonAddy should be automatically synchronized with the email provided by the proxy authentication headers.

Motivation / Use Case

Previously, when logging in via proxy authentication, the email address provided by the proxy was always synchronized with the user's default recipient email.

This behavior can be undesirable when users prefer to use a different email address to log into their authentication provider (e.g., Authelia, Authentik, etc.) than the one they want to use as their actual forwarding recipient in AnonAddy. This change allows users and administrators to disable this automatic synchronization to decouple the authentication email from the AnonAddy recipient email.

Changes

• .env.example & config/anonaddy.php: Added the ANONADDY_PROXY_AUTHENTICATION_SYNC_EMAIL environment variable and config option.
• ProxyAuthentication.php: Updated the proxy authentication middleware to check the new configuration and skip the updateDefaultRecipientIfNeeded logic when shouldSyncEmail is set to false.