Add docs for JSONRPC API. (#4810)

* Add docs for JSONRPC API.

* Some manual improvements

* Add to menu and clean up organization and formatting errors.

* fixed some links

* some formatting

* some formatting

* Fix spelling errors

---------

Co-authored-by: Sven Reichel <github-sr@hotmail.com>

Author: colinmollenhour

.github/spellcheck-wordlist.txt

@@ -1,6 +1,9 @@
 ACL
 ActionScript
+analytics
 bool
+boolean
+backorders
 Braintree
 Browsersync
 Captcha
@@ -10,6 +13,7 @@ CMS
 Cron
 CVE
 CodeQL
+config
 DevOps
 DDEV
 DNS
@@ -18,10 +22,13 @@ EAV
 Emmet
 FireGento
 FPC
+frontend
 Gitpod
 HiPay
 Homebrew
 HMAC
+HTTP
+HTTPS
 ImageMagick
 IntelliSense
 jQuery
@@ -50,19 +57,25 @@ PHPStan
 PhpStorm
 PHPUnit
 PLAINTEXT
+programmatically
 RCE
 reCaptcha
 Redis
 RPC
 RSS
 RWD
+runtime
 SCSS
 SHA
+sku
+SKU
+SKUs
 SMTP
 SSL
 TinyMCE
 toc
 URI
+un
 Varien
 VMware
 WAMP