Add TFE integration for backend and CICD

[lnesteroff]

Adding option to define (specifically terraform cloud) custom backbends. Also allows configuring TFE for CICD with the project attribute for read only and the workspace attribute for write.

Example var:

cicd_backends = {
  terraform = {
    organization = "your-terraform-organization"
    workspaces = {
      bootstrap = {
        tags = ["bootstrap", "tag1"]
      }
      resman = {
        name = "resman-workspace"
      }
      tenant-factory = {
        project = "tenant-project"
      }
      vpcsc = {
        name = "vpcsc-workspace"
      }
    }
    hostname = "app.terraform.io"
  }
}

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Checklist

I applicable, I acknowledge that I have:

• Read the contributing guide
• Ran terraform fmt on all modified files
• Regenerated the relevant README.md files using tools/tfdoc.py
• Made sure all relevant tests pass

[ludoo]

This will need to be integrated in the large PR for the next version of resman. Great job BTW :)