Gatsby-theme-novela: Add gatsby-remark-social-cards plugin

[dennismorello]

Is your feature request related to a problem? Please describe.
When embedding blog posts on social networks like LinkedIn, Twitter and Facebook, metadata on social card are poor and there is no thumbnail.

Describe the solution you'd like
It would be great if all the <meta .../> tags needed to build nice social cards were automatically generated. All the required data is already present in the frontmatter of each post, so adding a Remark plugin such gatsby-remark-social-cards should be easy.

Describe alternatives you've considered
Nothing.

Additional context
No additional context is required.

[jpvalery]

Could you open a PR to add this feature?

[dennismorello]

@jpvalery, @brotzky I am working on it

[mostafachatillon]

@dennismorello did you finish this feature? I also need it, how can I help?

[aleccool213]

Hmm, this shouldn't be needed. I was confused by this request as it is working for me just fine.

Here is the code for reference: https://github.com/narative/gatsby-theme-novela/blob/8a4a9b145954c2bc92a949d8b04fb95bf2ebdf00/%40narative/gatsby-theme-novela/src/components/SEO/SEO.tsx#L91