initial support for RPMs (#130)

cmd/cli/app/pflags.go

cmd/cli/app/pflags_test.go

cmd/cli/app/upload.go

cmd/cli/app/verify.go

cmd/server/app/serve.go

go.mod

go.sum

openapi.yaml

pkg/generated/models/proposed_entry.go

pkg/generated/models/rpm.go

pkg/generated/models/rpm_schema.go

pkg/generated/models/rpm_v001_schema.go

pkg/generated/restapi/embedded_spec.go

pkg/pki/pgp/pgp.go

pkg/types/rekord/rekord.go

pkg/types/rekord/rekord_test.go

pkg/types/rpm/rpm.go

pkg/types/rpm/rpm_schema.json

pkg/types/rpm/rpm_test.go

pkg/types/rpm/v0.0.1/entry.go