implements generic lookups into gossip crds table (#18765)

This commit adds CrdsEntry trait which allows generic lookups into crds
table. For example to get ContactInfo or LowestSlot associated with a
Pubkey, the lookup code would be respectively:
   crds.get::<&ContactInfo>(pubkey)
   crds.get::<&LowestSlot>(pubkey)

gossip/benches/crds_shards.rs

@@ -21,7 +21,7 @@ fn new_test_crds_value<R: Rng>(rng: &mut R) -> VersionedCrdsValue {
     let label = value.label();
     let mut crds = Crds::default();
     crds.insert(value, timestamp()).unwrap();
-    crds.get(&label).cloned().unwrap()
+    crds.get::<&VersionedCrdsValue>(&label).cloned().unwrap()
 }
 
 fn bench_crds_shards_find(bencher: &mut Bencher, num_values: usize, mask_bits: u32) {