[CT-1025] Should adapters be loaded earlier?

While looking at #5620, the fact that adapters are [loaded only as part of ConfiguredTask](https://github.com/dbt-labs/dbt-core/blob/43e3fc22c4eae4d3d901faba05e33c40f1f1dc5a/core/dbt/task/base.py#L175-L181) came up. This means that anywhere in the codebase that uses [get_adapter_package_names](https://github.com/dbt-labs/dbt-core/blob/43e3fc22c4eae4d3d901faba05e33c40f1f1dc5a/core/dbt/adapters/factory.py#L150) will not have access to the packages that adapters use.

This ticket tracks the effort around finding out if this behavior should be modified or remain as is.