Add Plugins Page to microsite (#2144)

* Add Plugins Page to microsite

* Updates to microsite Plugins Page

* Correct plugin authors and documentation links
* Add category to UI
* Move documentation from README to the docs website
* Use external urls for logos

* Updates to microsite Plugins Page

* trailing whitespace
* Run prettier on new markdown

* Updates to microsite Plugins Page

* Move plugins link
* Clarify category field

* Updates to microsite Plugins Page

* Add authorUrl field to plugin config
* Render author as a muted link like those in the site map

* Updates to microsite Plugins Page

* Add authorUrl field to example in docs

* Updates to microsite Plugins Page

* Add npmPackageName field - intended for future use

* Updates to microsite Plugins Page

* Add npmPackageName field - intended for future use

* Updates to microsite Plugins Page

* Use correct docs link

microsite/sidebars.json

@@ -91,7 +91,7 @@
       {
         "type": "subcategory",
         "label": "Publishing",
-        "ids": ["plugins/publishing", "plugins/publish-private"]
+        "ids": ["plugins/publishing", "plugins/publish-private", "plugins/add-to-marketplace"]
       }
     ],
     "Configuration": [