feat: added base api for xblocks in front

[holaontiveros]

This is a temporary PR so I can better review the changes, this is pointing to WGU EDX master so we SHOULD NOT merge it.

What was done?

• Added multi URL config so we can have the old por 1996 and the new port 8080 at the same time
• Added xblock handler get_contentthat returns the content and required info to be able to render it
• HTML xblock and video xblock got the new get_content handler

The response for the get_contenthandler will look like:

export interface XblockContent<TContent = string, TMetadata = XblockContentMetadata> {
  content: TContent,
  content_type: string,
  display_name: string,
  block_id: string,
  block_type: string,
  metadata: TMetadata,
  can_complete_on_view: boolean,
}

The content and Metadata can change depending on the Xblock to fit the right type of info required to render it