End point for autocomplete list

This MR creates a new endpoint for the search autocomplete feature

How to test

Follow the project setup instructions at the READme file. Make sure you use the e docs as the indexation folder

After your flask server is running assert that:

• A new endpoint successfully returns at /en/autocomplete
• The new endpoint returns gzip content
• The autocomplete list is good enough to be usable on the search feature at https://gitlab.e.foundation/e/documentation/user/-/merge_requests/480