Add redshift copy support for role-based credential string

[dlstadther]

Redshift copy supports key-based (with optional session token) or role-based credentials. This PR adds support for role-based credentials, making them the default choice if both role- and key-based are provided (since they are more restrictive and thus secure), and refactors implementation of optional session token for the key-based credential string.

Description

• Added two new properties aws_account_id and aws_arn_role_name
• Changed aws_access_key_id and aws_secret_access_key from @abc.abstractproperty to @property
  • Added possible NotImplementedError when no pair of credentials are provided to account for the lack of @abc.abstractproperty pair of credentials
• Defaults to role-based creds if both pairs are provided.
• Added test to ensure that NotImplementedError raises if no pair of creds are provided.

Motivation and Context

Transitioning to the use of role-based cred string for redshift copy. Maintain key-based creds. Refactor key-based session token.

Have you tested this? If so, how?

Single unit test for ensuring exception is raised if no pair of creds are provided.

Actual success of use has been verified for the 4 (most likely) cases:

• role-based and key-based are provided (role is used)
• key-based only
• role-based only
• neither (exception is raised)

[mention-bot]

@dlstadther, thanks for your PR! By analyzing the history of the files in this pull request, we identified @fordb, @rantav and @kianho to be potential reviewers.

[dlstadther]

These commits can and should be squashed prior to merge (assuming all tests pass).

[dlstadther]

Review request: @fordb @rantav @steenzout @ddaniels888 @moandcompany

Thanks

[dlstadther]

@Tarrasch I'm not sure what to do here. No one with Luigi Redshift experience seems to want to review. Suggestions?

[Tarrasch]

A coworker can review, if that's possible. If not, I'm fine with merging this after 2 weeks of no volunteered reviewing. :)

[dlstadther]

I'm a bit of a one-man band. So i'll wait a bit longer before merging. Thanks!

[dlstadther]

It's now been three week with no reviews. I'll be merging now!