[proxy] add metrics for caches (#12752)

Exposes metrics for caches. LKB-2594

This exposes a high level namespace, `cache`, that all cache metrics can
be added to - this makes it easier to make library panels for the caches
as I understand it.

To calculate the current cache fill ratio, you could use the following
query:

```
(
    cache_inserted_total{cache="node_info"}
  - sum (cache_evicted_total{cache="node_info"}) without (cause)
)
  / cache_capacity{cache="node_info"}
```

To calculate the cache hit ratio, you could use the following query:

```
  cache_request_total{cache="node_info", outcome="hit"}
/ sum (cache_request_total{cache="node_info"}) without (outcome)
```

proxy/src/cache/node_info.rs

@@ -1,7 +1,8 @@
-use crate::cache::common::Cache;
+use crate::cache::common::{Cache, count_cache_insert, count_cache_outcome, eviction_listener};
 use crate::cache::{Cached, ControlPlaneResult, CplaneExpiry};
 use crate::config::CacheOptions;
 use crate::control_plane::NodeInfo;
+use crate::metrics::{CacheKind, Metrics};
 use crate::types::EndpointCacheKey;
 
 pub(crate) struct NodeInfoCache(moka::sync::Cache<EndpointCacheKey, ControlPlaneResult<NodeInfo>>);
@@ -19,18 +20,30 @@ impl Cache for NodeInfoCache {
 impl NodeInfoCache {
     pub fn new(config: CacheOptions) -> Self {
         let builder = moka::sync::Cache::builder()
-            .name("node_info_cache")
+            .name("node_info")
             .expire_after(CplaneExpiry::default());
         let builder = config.moka(builder);
+
+        if let Some(size) = config.size {
+            Metrics::get()
+                .cache
+                .capacity
+                .set(CacheKind::NodeInfo, size as i64);
+        }
+
+        let builder = builder
+            .eviction_listener(|_k, _v, cause| eviction_listener(CacheKind::NodeInfo, cause));
+
         Self(builder.build())
     }
 
     pub fn insert(&self, key: EndpointCacheKey, value: ControlPlaneResult<NodeInfo>) {
+        count_cache_insert(CacheKind::NodeInfo);
         self.0.insert(key, value);
     }
 
-    pub fn get(&'static self, key: &EndpointCacheKey) -> Option<ControlPlaneResult<NodeInfo>> {
-        self.0.get(key)
+    pub fn get(&self, key: &EndpointCacheKey) -> Option<ControlPlaneResult<NodeInfo>> {
+        count_cache_outcome(CacheKind::NodeInfo, self.0.get(key))
     }
 
     pub fn get_entry(