Update terraform-validator version, instructions and CMEK bucket

[daniel-cit]

This PR:

• Updates the version of terraform-validator used to version 2021-03-22
• Update the README instructions regarding manual execution of terraform-validator

This PR also replaces the module used in the creation of the Google Cloud Storage bucket in the CMEK examples in the 4-projects environments.

From the main module

terraform-example-foundation/4-projects/business_unit_1/production/example_storage_cmek.tf

Line 69 in 137a379

source = "terraform-google-modules/cloud-storage/google"

to the simple bucket module

   source             = "terraform-google-modules/cloud-storage/google//modules/simple_bucket"

This is necessary because the way the main module construct the bucket attribute in the context of a random bucket name

locals {
...
  names_set    = toset(var.names)
...
resource "google_storage_bucket" "buckets" {
  for_each = local.names_set
...
  uniform_bucket_level_access = lookup(
    var.bucket_policy_only,
    lower(each.value),
    true,
  )

makes the after state of the bucket to be known only after apply which make terraform-validator crash.

Running the terraform-validator version in the master branch
which has the bugfix for the crash, terraform-validator rises a false positive.

Found Violations:

Constraint GCPStorageBucketPolicyOnlyConstraintV1.require_bucket_policy_only on resource //storage.googleapis.com/placeholder-fgDsc2WD: //storage.googleapis.com/placeholder-fgDsc2WD does not have bucket policy only enabled.

both issues, the crash and the false positive do not happen when using the simple bucket module

This change can be made because the CMEK creates a single bucket.

[daniel-cit]

@bharathkkb rebased to main branch