feat: account variable set

[jorrite]

This PR:

• Creates an account variable set.
• Creates the (at most) 3 variables (account, environment, workload_permissions_boundary_arn) inside the variable set, instead of passing them down to each workspace (and then creating individual workspace variables).
• Attach account variable set to all workspaces.

The net result here is a lot of less resources. With the following example: 20 workspaces, 4 environments (accounts), 4 variables:

	variables	variable sets	variable set attachments	total resources
before	320 [20×4×4]			320
after	16 [4×4]	4	80 [4x20]	100

Additionally, variables and an output is provider to add more variables to the same account variable set. The variables are there for things you know up front, the output is there for variables that might have values that relate to things you provision inside the accounts.

[github-actions]

Terraform Format and Style 🖌failure

Terraform Initialization ⚙️``

Terraform Lint 📖skipped

Terraform Validation 🤖skipped

Validation Output

[jorrite]

Oh, this entire change is dependent on schubergphilis/terraform-aws-mcaf-workspace#62. I've pinned on the git hash 6f6c0c8 for the workspace module. Once that PR is merged and has a stable tag, that will need to get updated here, of course.

[jorrite]

Updated the OP to reflect that this PR isn't a hybrid anymore, it changes the default behavior. ☝️.