Trigger RPC notifications after block commitment cache update (#10077)

* Fixup commitment-aggregation metric

* Trigger notifications after commitment-cache update

* Fixup fn name

* Add single-confirmation commitment level

* Rename to highest_confirmed_slot

* Pass commitment-cache info directly to notifications

* Use match

* Update commitment docs

* Update out of date pubsub docs

sdk/src/commitment_config.rs

@@ -31,6 +31,12 @@ impl CommitmentConfig {
         }
     }
 
+    pub fn single() -> Self {
+        Self {
+            commitment: CommitmentLevel::Single,
+        }
+    }
+
     pub fn ok(self) -> Option<Self> {
         if self == Self::default() {
             None
@@ -46,4 +52,5 @@ pub enum CommitmentLevel {
     Max,
     Recent,
     Root,
+    Single,
 }