fix: allow cosign opts to be empty in aqua

The opts attribute on cosign check for aqua is optional.
If not provided it will make the package resolution fail.
This patch makes it optional and provide an empty array if key is not
found.

src/aqua/aqua_registry.rs

@@ -123,6 +123,7 @@ pub struct AquaCosign {
     pub signature: Option<AquaCosignSignature>,
     pub key: Option<AquaCosignSignature>,
     pub certificate: Option<AquaCosignSignature>,
+    #[serde(skip_serializing_if = "Vec::is_empty", default)]
     opts: Vec<String>,
 }