[c][p][t] Add platform seal on signature metadata

auth/signature.go

auth/signature_test.go

dfssc/api/client.pb.go

dfssc/api/client.proto

dfssc/sign/promises.go

dfssc/sign/starter.go

dfssp/api/platform.pb.go

dfssp/api/platform.proto

dfssp/server/server.go

dfsst/entities/archivesManager.go

dfsst/entities/archivesManager_test.go

dfsst/entities/authContainer.go

dfsst/entities/check_request.go

dfsst/entities/check_request_test.go

dfsst/entities/signatureArchives.go

dfsst/server/server.go