Move OSBuildMetadataToRPMs and PackageMetadataToSignature to osbuild2

Move `OSBuildMetadataToRPMs()` and `PackageMetadataToSignature()`
functions from the `rpmmd` package to `osbuild2` package to prevent
import cycles while de-duplicating `rpmStageInputs()` function from
`stage_inputs.go` of distro definitions.

Rename `PackageMetadataToSignature()` to
`RPMPackageMetadataToSignature()`, since it takes specifically
`RPMPackageMetadata` type as an argument.

Adjust affected parts of code (unit tests, cloudapi, worker).

Signed-off-by: Tomas Hozza <thozza@redhat.com>

internal/cloudapi/v2/v2.go

@@ -1013,7 +1013,7 @@ func stagesToPackageMetadata(stages []osbuild.RPMStageMetadata) []PackageMetadat
 					Epoch:     rpm.Epoch,
 					Arch:      rpm.Arch,
 					Sigmd5:    rpm.SigMD5,
-					Signature: rpmmd.PackageMetadataToSignature(rpm),
+					Signature: osbuild.RPMPackageMetadataToSignature(rpm),
 				},
 			)
 		}