Document environment variables for logging node heap stats

overview.md

@@ -356,6 +356,8 @@ The environmental variables for the clearlydefined-api-dev App Service include:
 * HARVEST_QUEUE_PREFIX
 * HARVEST_QUEUE_PROVIDER
 * HARVESTER_PROVIDER
+* LOG_NODE_HEAPSTATS
+* LOG_NODE_HEAPSTATS_INTERVAL_MS
 * NODE_ENV
 * RATE_LIMIT_MAX
 * RATE_LIMIT_WINDOW
@@ -535,6 +537,29 @@ This is the prefix we use for queues that we use for harvesting. In this case, i
 
 This indicates what type of service we use for harvesting, in this case it's **crawlerQueue**, which corresponds with the [crawlerQueue harvest provider](https://github.com/clearlydefined/service/blob/master/providers/harvest/crawlerQueue.js)
 
+**LOG_NODE_HEAPSTATS**
+This is an optional flag to `enable` logging of Node's `v8` module's memory usage data using the `getHeapSpaceStatistics` and `getHeapStatistics()` functions.
+
+Value is either `true` or `false`
+> Note: if this env var is not present, it equates to `false`
+
+> example:  
+> `LOG_NODE_HEAPSTATS` = `true`
+
+- [Node.js v8 engine docs - getHeapSpaceStatistics()](https://nodejs.org/docs/v22.12.0/api/v8.html#v8getheapspacestatistics)
+
+- [Node.js v8 engine docs - getHeapStatistics()](https://nodejs.org/docs/v22.12.0/api/v8.html#v8getheapstatistics)
+
+**LOG_NODE_HEAPSTATS_INTERVAL_MS**
+
+This is an optional environment variable that sets the interval to log heap statistics (When enabled).
+
+Value is a number in `ms` (`milliseconds`).
+> NOTE: The default value is `30000` ms (`30` seconds)
+
+> example:   
+> `LOG_NODE_HEAPSTATS_INTERVAL_MS` = `10000`
+
 **MULTIVERSION_CURATION_FF**
 
 This is a feature flag that indicates whether the [Multi-version curation feature](https://github.com/clearlydefined/service/pull/810) is active.