Add managed folders support to gcs module

[juliocc]

• Add support for managed folders
• Add support for RPO
• Make STANDARD the default storage class
• Add iam_by_principals

[ludoo]

very nice, my only nit is on Keys must end in /, can we interpolate it and have more readable keys? ignore me ofc if the current approach makes more sense

[juliocc]

very nice, my only nit is on Keys must end in /, can we interpolate it and have more readable keys? ignore me ofc if the current approach makes more sense

Removed the need for the trailing /