Feature: Support IAM Conditions

[lawliet89]

I would like to request for support of Cloud IAM conditions in the rolesets. Conditions are attached to the IAM bindings themselves and would be useful to further restrict what the rolesets can and cannot do.

Suggested HCL Syntax

resource "projects/X" {
    roles = [
        "roles/viewer",
    ]

       condition "roles/viewer" {
        title = "A conditional IAM title"
        description = "A conditional IAM description"
        expression = "ResourceA==ResourceB"
       }

       condition "roles/editor" {
        title = "A conditional IAM title"
        description = "A conditional IAM description"
        expression = "ResourceA==ResourceB"
       }
}

[cvolante54]

I think this feature would be very beneficial. My understanding is that only work on the hcl parsing needs to be done to support this feature since https://github.com/hashicorp/vault-plugin-secrets-gcp/pull/77 already updated the policy object