doc: Add maxTotalSockets option to agent constructor

doc/api/http.md

@@ -113,6 +113,9 @@ http.get({
 <!-- YAML
 added: v0.3.4
 changes:
+  - version: v14.5.0
+    pr-url: https://github.com/nodejs/node/pull/33617
+    description: Add `maxTotalSockets` option to agent constructor.
   - version: v14.5.0
     pr-url: https://github.com/nodejs/node/pull/33278
     description: Add `scheduling` option to specify the free socket
@@ -136,6 +139,10 @@ changes:
   * `maxSockets` {number} Maximum number of sockets to allow per
     host. Each request will use a new socket until the maximum is reached.
     **Default:** `Infinity`.
+  * `maxTotalSockets` {number} Maximum number of sockets allowed for
+    all hosts in total. Each request will use a new socket
+    until the maximum is reached.
+    **Default:** `Infinity`.
   * `maxFreeSockets` {number} Maximum number of sockets to leave open
     in a free state. Only relevant if `keepAlive` is set to `true`.
     **Default:** `256`.