[CT-909] Adapter Management works with Click

[iknox-fa]

User Story:
As a user of dbt, adapters continue to work as they do currently

Acceptance Criteria:

• The logic found in the adapter_management context manager is moved to the root click group and propagates down to all subcommands

[jtcohen6]

I agree with the scope of this ticket, which is that adapters should continue to work exactly as they do today, with the new CLI + top-level API.

One thing I wanted to share, in case it's interesting, is that I've been experimenting with making adapters less "global": https://github.com/dbt-labs/dbt-core/compare/jerco/experiment-deglobalize-adapters

The idea in that branch:

• Store adapter object on RuntimeConfig, instead of registering / loading from the global AdapterFactory
• The AdapterFactory is still the global registry for adapter plugins, which are library code (classes) used to create specific adapter objects. I think this is a safe assumption unless we’re going to be installing / adding new plugin code midway through dbt-core applications.

I think that's a path we should probably continue pursuing. It means that we might not need the same kind of adapter_management context management that we have currently, which requires us to reset adapters as the very first step. (We should still clean up connections at the end of every task/command.)

[iknox-fa]

@jtcohen6
I love the idea, but it ended up being only one line of code to move this to the Click world as-is so the global state persists for now.

[jtcohen6]

@iknox-fa great solution to the scope of this initial ticket!