Add documentation for environment variables (#177)

* Add documentation for BATCH_RATE_LIMIT_MAX and BATCH_RATE_LIMIT_WINDOW

* Document environment variables for logging node heap stats

Author: qtomlinson

service_config/service.md

@@ -7,6 +7,8 @@
     - [AUTH\_CURATION\_TEAM](#auth_curation_team)
     - [AUTH\_GITHUB\_CLIENT](#auth_github_client)
     - [AUTH\_HARVEST\_TEAM](#auth_harvest_team)
+    - [BATCH_RATE_LIMIT_MAX](#batch_rate_limit_max)
+    - [BATCH_RATE_LIMIT_WINDOW](#batch_rate_limit_window)
     - [CACHING\_PROVIDER](#caching_provider)
     - [CACHING\_REDIS\_SERVICE](#caching_redis_service)
     - [CRAWLER\_API\_AUTH\_TOKEN\*\*](#crawler_api_auth_token)
@@ -32,6 +34,8 @@
     - [HARVEST\_QUEUE\_PROVIDER](#harvest_queue_provider)
     - [HARVEST\_QUEUE\_PREFIX\*\*](#harvest_queue_prefix)
     - [HARVESTER\_PROVIDER](#harvester_provider)
+    - [LOG\_NODE\_HEAPSTATS](#log_node_heapstats)
+    - [LOG\_NODE\_HEAPSTATS\_INTERVAL\_MS](#log_node_heapstats_interval_ms)
     - [MULTIVERSION\_CURATION\_FF](#multiversion_curation_ff)
     - [NODE\_ENV](#node_env)
     - [RATE\_LIMIT\_MAX](#rate_limit_max)
@@ -94,9 +98,13 @@ 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
+* BATCH_RATE_LIMIT_MAX
+* BATCH_RATE_LIMIT_WINDOW
 * SEARCH_AZURE_API_KEY
 * SEARCH_AZURE_SERVICE
 * SEARCH_PROVIDER
@@ -312,6 +320,28 @@ Important to ensure that any other instances of production crawlers that use the
 
 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.
@@ -334,6 +364,14 @@ When we [use this value in the code](https://github.com/clearlydefined/service/b
 
 So, one IP address can only call the ClearlyDefined API 500 times every 300 seconds.
 
+### BATCH_RATE_LIMIT_MAX
+
+Defines the maximum number of requests allowed from a single IP to the batch endpoints within the batch rate limit window.
+
+### BATCH_RATE_LIMIT_WINDOW
+
+Defines the time window (in seconds) used to apply `BATCH_RATE_LIMIT_MAX` for batch endpoints. This value is multiplied by 1000 internally to convert to milliseconds (same as `RATE_LIMIT_WINDOW`)
+
 ### SEARCH_PROVIDER
 
 We use [Azure Cognitive Search](https://docs.microsoft.com/en-us/azure/search/search-what-is-azure-search) to power ClearlyDefined's Search functionality, in this case this is indicated with the string "azure".