feat(v2): improve seo (#1588)

* feat(v2): improve seo

- Add doc specific seo information
- Add twitter meta tags to seo in theme Layout

* Cannot use svg in SEO image

* Add docs about SEO

* add site default image for seo

* Resolve PR discussion

* Add `image` to config optional fields

* Use theme config instead of root config for image, rename in front matter

* Use absolute url for image (wont work on preview)

* update docs for frontmatter field for seo

* refactor

* pages seo

* fix

* nits again'

website/docusaurus.config.js

@@ -33,6 +33,7 @@ module.exports = {
     ],
   ],
   themeConfig: {
+    image: 'img/docusaurus.png',
     gtag: {
       trackingID: 'UA-141789564-1',
     },