Replace db/schema.rb with structure.sql

[sauloperez]

Description

The way we aim to migrate from ElasticSearch to PostgreSQL full-text search requires a function and a trigger, which is not supported by default Rails Ruby schema format.

This change should be a refactor. No behavior change at all. That's what we'll to confirm in production.

What to do

We just need to bring the change done in #465 in a new branch that only changes the schema.

Some time ago I came across a blog that would be great to check when doing this: https://blog.appsignal.com/2020/01/15/the-pros-and-cons-of-using-structure-sql-in-your-ruby-on-rails-application.html