doc: include http2.md in all.md

Backport-PR-URL: #14813
Backport-Reviewed-By: Anna Henningsen <[email protected]>
Backport-Reviewed-By: Timothy Gu <[email protected]>

PR-URL: #14239
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Matteo Collina <[email protected]>

Author: jasnell

doc/api/all.md

@@ -19,6 +19,7 @@
 @include fs
 @include globals
 @include http
+@include http2
 @include https
 @include inspector
 @include intl