Add service whitelist functionality for OPNsense services

[somnium78]

Problem

The current OPNsense service check in CheckMK reports all stopped services as critical errors, even when services are intentionally disabled by the administrator.

Key issues:

• No mechanism to whitelist or exclude specific services from monitoring
• The check aggregates all services into a single CheckMK service, making it impossible to use CheckMK's built-in "Disabled Services" rules
• Results in false-positive alerts for legitimately stopped services (e.g., unbound, ntopng, haproxy)
• Administrators have no way to suppress these alerts without disabling the entire service check

Solution

This PR adds a whitelist functionality that allows administrators to exclude specific services from error reporting:

• Automatically creates /usr/local/etc/checkmk_service_whitelist.conf on first run
• Services listed in the whitelist file are excluded from critical status
• Adds new whitelisted_services metric for monitoring
• Maintains full backward compatibility (works without whitelist file)
• Simple text-based configuration (one service name per line)

Edit:

• changed "whitelist" to "blacklist"

[DerMistkaefer]

When the whitelist works as a blacklist we should call it blacklist.

Also please remove or change the german comments.