Database auto-upgrade

[vikman90]

Main task	Component
#1904	Wazuh DB

Issue #1904 introduces a change in the Wazuh DB schema for agents. These databases must be persistent from Wazuh v3.7.0. No newer version would be able to use a database with a schema version of 3.7.0.

That's why we need to implement an automatic upgrading procedure.

Brainstorming

• SQLite allows deleting some columns from a table. It also allows appending a new column, but there is no way to alter the table's primary key. When we want to update a table, maybe we would have to:
  1. Rename the table.
  2. Create a new table that will replace the previous one.
  3. Copy every tuple from the old table to the new table.
  4. Drop the old table.
• It's easier to implement a progressive update. For instance, if we want to upgrade from 3.7.0 to 3.9.0, we may make two steps:
  1. Upgrade from 3.7.0 to 3.8.0.
  2. Upgrade from 3.8.0 to 3.9.0.
• Current databases have a table including the release version. I think it will be easier to include a DB version number —independent from the release version— to perform upgrades.