Add Elixir Documentation to the Unkey site

[glamboyosa]

Closes

Closes #48

Description

This PR adds Elixir documentation to the Unkey site for the #48.

Testing Plan

• Go to the docs site
• Go to the libraries section
• Under the Elixir section there should be overview docs which includes a brief overview.
• Go to the functions subdir, it should include all the Elixir SDK methods (can be corroborated with the Hexdocs )

[vercel]

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