chore: upgrade lru-cache; replace use of async-cache (#3610)

lru-cache@7 added support for async fetching, and async-cache
was deprecated

See https://github.com/isaacs/node-lru-cache#fetchmethod-read-only
for the best docs for using lru-cache for async caching.

Refs: #2760

lib/opentelemetry-metrics/ElasticApmMetricExporter.js

@@ -14,7 +14,7 @@ const {
   DropAggregation,
   DataPointType,
 } = require('@opentelemetry/sdk-metrics');
-const LRU = require('lru-cache');
+const { LRUCache } = require('lru-cache');
 
 /**
  * The `timestamp` in a metricset for APM Server intake is "UTC based and
@@ -102,8 +102,8 @@ class ElasticApmMetricExporter {
     this._sumAggregation = new SumAggregation();
     this._lastValueAggregation = new LastValueAggregation();
     this._dropAggregation = new DropAggregation();
-    this._attrDropWarnCache = new LRU({ max: 1000 });
-    this._dataPointTypeDropWarnCache = new LRU({ max: 1000 });
+    this._attrDropWarnCache = new LRUCache({ max: 1000 });
+    this._dataPointTypeDropWarnCache = new LRUCache({ max: 1000 });
   }
 
   /**