[ADAP-926] [Feature] IAM authentication - make 'user' an optional property

[Jake-Gillberg]

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

Redshift supports IAM authentication without a redshift user name via GetClusterCredentialsWithIAM, which

Returns a database user name and temporary password with temporary authorization to log in to an Amazon Redshift database. The database user is mapped 1:1 to the source AWS Identity and Access Management (IAM) identity.

It would be awesome if dbt-redshift supported this authentication method as well, allowing for user to be optional configuration when using method: iam for authentication.

Describe alternatives you've considered

No response

Who will this benefit?

No response

Are you interested in contributing this feature?

No response

Anything else?

No response

[misteliy]

Is there any progress here?