[Feature] Rename method to authenticator

[VersusFacit]

Is this your first time submitting a feature request?

• I have read the expectations for open source contributors
• I have searched the existing issues, and I could not find an existing issue for this feature
• I am requesting a straightforward extension of existing dbt-redshift functionality, rather than a Big Idea better suited to a discussion

Describe the feature

Recently, in an internal discussion we referred to dbt-redshift's authenticator config param. We then realized that the param is called method on that adapter. Let's align the two names by migrating the param with use of a behavior flag to derisk.

The work in dbt-redshift will be to rename the parameter in the Credentials class and all referencing tests.

Describe alternatives you've considered

Leave it as is

Who will this benefit?

In a multi-platform workflow, having a standard configuration nameset leads to a more intuitive (and satisfying) user experience. This PR continues our tend of standardizing name fields across adapters.

Are you interested in contributing this feature?

of course

Anything else?

We will need to consider how this affects Cloud profile generation. It may not. But there's a minor chance it might and we should be conscious of that possibility.

This will require a docs update as well.