JS: document new eventHistoryTTL and minBidCacheTTL settings (prebid#4884)

Author: dgirardi

dev-docs/publisher-api-reference/setConfig.md

@@ -24,6 +24,8 @@ Core config:
 * [Turn on send all bids mode](#setConfig-Send-All-Bids)
 * [Configure send bids control](#setConfig-Send-Bids-Control)
 * [Bid cache](#setConfig-Use-Bid-Cache)
+* [Minimum bid cache TTL](#setConfig-minBidCacheTTL)
+* [Event history TTL](#setConfig-eventHistoryTTL)
 * [Set the order in which bidders are called](#setConfig-Bidder-Order)
 * [Set the page URL](#setConfig-Page-URL)
 * [Set price granularity](#setConfig-Price-Granularity)
@@ -279,6 +281,33 @@ pbjs.setConfig({
 });
 ```
 
+#### Minimum bid cache TTL
+
+<a id="setConfig-minBidCacheTTL"></a>
+
+By default, Prebid keeps every bid it receives stored in memory until the user leaves the page. This can cause high memory usage on long-running single-page apps; you can configure Prebid to drop stale bids from memory with `minBidCacheTTL`:
+
+```javascript
+pbjs.setConfig({
+  minBidCacheTTL: 60  // minimum time (in seconds) that bids should be kept in cache
+})
+```
+
+When set, bids are only kept in memory for the duration of their TTL or the value of `minBidCacheTTL`, whichever is greater. Setting `minBidCacheTTL: 0` causes bids to be dropped as soon as they expire.
+
+#### Event history TTL
+
+<a id="setConfig-eventHistoryTTL"></a>
+
+By default, Prebid keeps in memory a log of every event since the initial page load, and makes it available to analytics adapters and [getEvents()](/dev-docs/publisher-api-reference/getEvents.html).
+This can cause high memory usage on long-running single-page apps; you can set a limit on how long events are preserved with `eventHistoryTTL`:
+
+```javascript
+pbjs.setConfig({
+  eventHistoryTTL: 60 // maximum time (in seconds) that events should be kept in memory
+})
+```
+
 #### Bidder Order
 
 Set the order in which bidders are called: