Add pacman (alpm) parser support (#943)

Co-authored-by: Christopher Phillips <christopher.phillips@anchore.com>

syft/linux/identify_release.go

@@ -111,6 +111,10 @@ func parseOsRelease(contents string) (*Release, error) {
 		IDLike:           idLike,
 		Version:          values["VERSION"],
 		VersionID:        values["VERSION_ID"],
+		VersionCodename:  values["VERSION_CODENAME"],
+		BuildID:          values["BUILD_ID"],
+		ImageID:          values["IMAGE_ID"],
+		ImageVersion:     values["IMAGE_VERSION"],
 		Variant:          values["VARIANT"],
 		VariantID:        values["VARIANT_ID"],
 		HomeURL:          values["HOME_URL"],