enhancement(db): allow connection to be a function

[innerdvations]

What does it do?

Allow database connection functions in user configs without any breaking changes by adding a check in init to resolve the connection and configure the dialect.

There is no risk of a breaking change for anyone currently using connection objects because those will still always handled synchronously exactly as before.

Why is it needed?

https://github.com/strapi/strapi/issues/18474

Essentially, connection functions are a requirement for many database services that require refreshing access tokens rather than a fixed auth.

There is still a potential problem where if a plugin tries to address db.connection prior to init, it can now potentially fail, so connection functions will only be added as experimental and we can ban that practice and provide an alternate solution in v6 as a breaking change so that we can consider it stable.

How to test it?

experimental: 0.0.0-experimental.b391efb8ce3832d4f280928b99ef5cb9c228fdee npx create-strapi-app@0.0.0-experimental.b391efb8ce3832d4f280928b99ef5cb9c228fdee

Use a function in your database config connection instead of an object

Unit tests have been added

Related issue(s)/PR(s)

https://github.com/strapi/strapi/issues/18474

https://github.com/strapi/strapi/pull/18857

Docs PR: https://github.com/strapi/documentation/pull/2252

PR for Knex to fix Sqlite3 warning: https://github.com/knex/knex/pull/6136