Summary

Part of #94141
closes #81483

Get rid of /src/legacy

• Move the legacy logging registration to core's legacy service
• Move the remaining '/{path*}' route to core's app service
• Add the legacy logging schema to core's logging config
• Remove last utils from src/core/server/utils (fromRoot and pkg), replaced by using @kbn/utils instead
• Adapt and fix stuff

Checklist

• Unit or functional tests were updated or added to match the most common scenarios

Release Note

• The plugins.scanDirs configuration property has been deprecated and is no longer used.
• The server.maxPayloadBytes configuration property has been renamed server.maxPayload