Add back support for accessing AWS with an assumed role with an external ID

[misterpantz]

What is not working as you expected it?
I can't scan or query AWS with an assumed role with an external ID. I used to be able to do this with the --options flag but when we got rid of that, it seems we lost this capability.

Where on the platform does it happen?
cnquery, cnspec

How do we replicate the issue?
cnspec scan aws -h and notice that there is no flag for an external ID. I tried guessing a couple in case it just wasn't in the help, but no success.

Expected behavior (i.e. solution)
I expect an --external-id role or something similar.

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