chore: update perimeter_additional_members instructions

[romanini-ciandt]

Issue #936

This PR implements an update on perimeter_additional_members variable declaration in both 3-networks steps.

Basically, we want to avoid a situation where the user forget to uncomment a .tfvars line and because of that don't have access to a project protected by the VPC service controls. With this change, if the user forgets to fulfil the variable, an error will be raised during deploy process.

[rjerrems]

Rather than providing an uncommented bogus parameter, why don't we make it so that perimeter_additional_members has no default value, so that it errors out when not provided?

In that case, if a user does not want to provide any members they can add [""]

[romanini-ciandt]

@rjerrems thanks for your inputs!
In order to solve the #936 issue, I'm implementing a dummy value for perimeter_additional_members variable on .tfvars that should be replaced like we have for others required variables (i.e: in the same file we have example.com. for domain)

Nowadays, perimeter_additional_members variable doesn't have a default in variables.tf, so the current behavior is to have an error when not provided. The goal of this PR is to standardize the required variable's declaration in .tfvars and make all of them (the required ones) uncommented.

With this context, do you think that makes sense to keep this PR as is?

[rjerrems]

Ok thanks for the context - probably worth checking with @eeaton before merging to make sure it addresses the issue fully.

[eeaton]

This works for me. At a future date I'm planning on doing a more thorough review of the directions in README files for this type of usability challenge, but for the scope of issue #936 that I raised, this works.

[daniel-cit]

@gtsorbo this pull request edits README.md markdown files and common.auto.example.tfvars files that are not used in the integration build process.