Embed the Elastic global header on elastic.co/docs/api

## Problem

The experiences between http://elastic.co/docs and http://elastic.co/docs/api are completely different. When you navigate from http://elastic.co/docs to http://elastic.co/docs/api, it is clear you are leaving the elastic.coweb property.

## Solution

[Embedding Bump.sh in your own portal](https://docs.bump.sh/help/customization-options/embed-mode/)

Ideal embedded documentation behavior:

- It will properly display the Elastic Global header with the right branding, and allow data collection
- The Bump top bar will be removed, including the search
- Elastic search engine will be improved through meta filter

## Next steps

- [ ] Set up a reverse proxy of the origin (public hub example: https://bump.sh/elastic/hub/public-apis) to transform the response body. You'll find an example of a proxy (in NodeJS) that we could use to set up an Embed mode of the Bump documentation: https://gist.github.com/paulRbr/3af8e3af0a2450772fb1698bdd7e8910
- [ ] Change fonts in Staging to start testing injections
- [ ] Inject header in Staging to test the Embed mode
- [ ] Remove the [Bump.sh](http://bump.sh/) navigation in Staging
- [ ] Deploy Embed mode in production