Cleanup: refactor parsing and handling of Daemon config

* Merge `daemonconfig` into `daemon/config.go`
* Apply post-parsing default values in `NewDaemon` for DRY
* Command-line flags are defined and installed in `daemon.Config.InstallFlags` instead of in `main`

This depends on #7497
We could fallback to the last version handled by the server instead of producing  an error and hope it'll work. (it will most of the time, and in that case)