Adds SEO support for custom page meta

Proposal for supporting SEO meta tags for all the pages.

1. Default values for SEO meta tags, og:title and og:description, are pulled from the .vuepress/config.js file.

2. Customize the SEO values per page by adding YAML "frontmatter" to the top of the markdown pages.

Example:

See example implementation on the apply/registration.md file like so:

---
title: Applications for Fab Academy
description: The application process to join the Fab Academy course
---

# FAB ACADEMY 

### Applications for **Fab Academy 2022** are now OPEN!!

If you are interested in getting acquainted with....... <<etc rest of document>>

@lucianaa @bnore Let me know if this works.