Add feature to specify the allowed dhcp cidrs

[majst01]

To prevent unwanted machines to be reported

[majst01]

0059","BiosVersion":"","led":"Off"}                                                                                                                                                                                                                                              
Sep 05 05:39:06 eqx-mu4-mgmtserver01 docker[2079342]: {"level":"debug","timestamp":"2023-09-05T05:39:06Z","caller":"zap/zap.go:18","msg":"connect","board":"Vendor:UNKNOWN Model:"}                                                                                              
Sep 05 05:39:06 eqx-mu4-mgmtserver01 docker[2079342]: {"level":"error","timestamp":"2023-09-05T05:39:06Z","caller":"zap/zap.go:30","msg":"connect","unknown vendor":"UNKNOWN","stacktrace":"github.com/metal-stack/go-hal/pkg/logger/zap.(*ZapLogger).Errorw\n\tgithub.com/metal-
stack/[email protected]/pkg/logger/zap/zap.go:30\ngithub.com/metal-stack/go-hal/connect.OutBand\n\tgithub.com/metal-stack/[email protected]/connect/connect.go:66\ngithub.com/metal-stack/metal-bmc/internal/leases.(*ReportItem).EnrichWithBMCDetails\n\tgithub.com/metal-stack/metal-bm
c/internal/leases/bmc.go:11\ngithub.com/metal-stack/metal-bmc/internal/reporter.reporter.Run.func1\n\tgithub.com/metal-stack/metal-bmc/internal/reporter/reporter.go:76\ngolang.org/x/sync/errgroup.(*Group).Go.func1\n\tgolang.org/x/[email protected]/errgroup/errgroup.go:75"}      
Sep 05 05:39:06 eqx-mu4-mgmtserver01 docker[2079342]: {"level":"error","timestamp":"2023-09-05T05:39:06Z","caller":"leases/bmc.go:13","msg":"could not establish outband connection to device bmc","mac":"3c:ec:ef:da:b0:e7","ip":"10.1.3.19","err":"vendor unknown","stacktrace"
:"github.com/metal-stack/metal-bmc/internal/leases.(*ReportItem).EnrichWithBMCDetails\n\tgithub.com/metal-stack/metal-bmc/internal/leases/bmc.go:13\ngithub.com/metal-stack/metal-bmc/internal/reporter.reporter.Run.func1\n\tgithub.com/metal-stack/metal-bmc/internal/reporter/

[Gerrit91]

@mwindower FYI