fix: allow cosign opts to be empty in aqua (#4396)

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.

This address the issue described here:
#4092

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>,
 }