Add support for SQL queries

[Angelmmiguel]

Allow workers to interact with a SQL database via host functions. The worker will be able to connect to a DB that it's configured in the TOML file. This will allow to have a great data persistance and enable new use cases.

We want to ensure the capability-based model is respected here too. So, in the configuration we may state what are the operations a certain worker can do. For example, read, update, etc.

For now, this is a proposal. We will refine it over the time.