config: add "cert_subjects" alias for "princs" filters

The name "princs" does not make sense when TLS is used, so an alias
has been added:

[filter]
operation = "Only"
cert_subjects = [
    "win10.windomain.local",
]

common/src/models/config.rs

@@ -178,6 +178,7 @@ impl From<PrincsFilterOperation> for crate::subscription::PrincsFilterOperation
 #[serde(deny_unknown_fields)]
 struct PrincsFilter {
     pub operation: Option<PrincsFilterOperation>,
+    #[serde(alias = "cert_subjects")]
     pub princs: HashSet<String>,
 }