fix: system config webhook check

[cyl3x]

The WebhookSystemConfigHelper was fed with a wrongly structured config array. A correctly structured array is now used, in addition to:

• Check webhook only if a config value will change
• Check for all route expect our route which already handled it, catching also cases where the system config is written via commands or yaml

fixes shopware/shopware#7537

[mitelg]

thank you very much!