Add support for APK download URLs

Signed-off-by: Tushar Goel <tushar.goel.dav@gmail.com>

Author: TG1999

src/packageurl/contrib/purl2url.py

@@ -674,6 +674,11 @@ def build_apk_download_url(purl):
     repo = purl.qualifiers.get("repo")
     alpine_version = purl.qualifiers.get("alpine_version")
 
+    if not name or not version or not arch or not repo or not alpine_version:
+        raise ValueError(
+            "All qualifiers (arch, repo, alpine_version) and name/version must be present in apk purl"
+        )
+
     return (
         f"https://dl-cdn.alpinelinux.org/alpine/{alpine_version}/{repo}/{arch}/{name}-{version}.apk"
     )