Conditionally generate tfvars for non-core accounts

[dms1981]

This PR relates to #4139. As we make use of networking.auto.terraform.tfvars to share resources, it's not relevant to our core accounts and as such this PR makes its creation conditional.

• Updates the scripts that output this file to conditionally skip the creation when we read the account type from environments/*.json and see that they account-type value is core.
• Removes networking.auto.terraform.tfvars from core accounts.
• Adds defaults to base_variables.tf for both core-sandbox and core-vpc accounts to accommodate removal of tfvars.
• Tidies up some of core-sandbox account to remove some unused code and fix a broken data call.

[github-actions]

TFSEC Scan Success

Show Output

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TFSEC will check the following folders:

Checkov Scan Success

Show Output

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Checkov will check the following folders:

CTFLint Scan Success

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Setting default tflint config...
Running tflint --init...
Installing `terraform` plugin...
Installed `terraform` (source: github.com/terraform-linters/tflint-ruleset-terraform, version: 0.2.1)
tflint will check the following folders:

[github-actions]

TFSEC Scan Success

Show Output

*****************************

TFSEC will check the following folders:

Checkov Scan Success

Show Output

*****************************

Checkov will check the following folders:

CTFLint Scan Success

Show Output

*****************************

Setting default tflint config...
Running tflint --init...
Installing `terraform` plugin...
Installed `terraform` (source: github.com/terraform-linters/tflint-ruleset-terraform, version: 0.2.1)
tflint will check the following folders:

[markgov]

LGTM