Add support for adding new Nextcloud domains to existing HPB installa…

[warioishere]

This change makes the setup script re-runnable and adds the capability to add new Nextcloud domains to an existing High-Performance Backend setup without regenerating existing secrets.

Key features:

• Detection of existing HPB installation
• ADD_DOMAINS_MODE to preserve existing configuration and secrets
• Parsing of existing domains and secrets from configuration files
• Generation of new secrets only for newly added domains
• Appending new domains to existing secrets file with timestamp
• Support for both interactive and unattended modes
• Automatic detection of previously installed services

Changes made:

1. setup-nextcloud-hpb.sh:

   • Added is_hpb_installed() to detect existing installation
   • Added parse_existing_domains() to extract existing Nextcloud domains
   • Added parse_existing_secrets() to load existing domain secrets
   • Added parse_existing_global_secrets() to load Janus/TURN/hash/block keys
   • Added ADD_DOMAINS_MODE flag and detection logic in main()
   • Modified show_dialogs() to display existing domains when adding new ones
   • Auto-detect SERVER_FQDN from existing configuration in ADD_DOMAINS_MODE
   • Skip service selection dialog in ADD_DOMAINS_MODE
   • Prevent overwriting secrets file header in ADD_DOMAINS_MODE

2. src/setup-signaling.sh:

   • Modified signaling_step4() to handle existing + new domains
   • Preserve existing secrets for existing domains
   • Generate new secrets only for new domains
   • Modified signaling_write_secrets_to_file() to append new domains with timestamp instead of overwriting entire file

3. src/setup-collabora.sh:

   • Modified collabora_step4() to include existing domains when regenerating Collabora configuration with new domains

4. settings.sh:

   • Added ADD_DOMAINS_MODE configuration option with documentation

Usage:

• Fresh install: Run script normally
• Add domains: Run script again, it will detect existing installation and prompt to add new domains, preserving all existing secrets
• Unattended add: Set ADD_DOMAINS_MODE=true in settings file

The secrets file now maintains a complete history with new domains appended at the end with timestamps for easy tracking.