Fix pgadmin for deployment with vpc

[dkatzz]

Description

We were getting an error when running pgadmin:

╷
│ Error: Invalid value for input variable
│ 
│   on main.tf line 169, in module "pgadmin":
│  169:   subnet_ids      = local.vpc_private_subnets
│ 
│ The given value is not suitable for module.pgadmin[0].var.subnet_ids
│ declared at ../../modules/pgadmin/variables.tf:47,1-22: element 0: string
│ required.

By pointing at the ID variable instead, we are successfully able to create pgadmin resources. Note: this doesn't change anything for non-vpc enabled deployments, since _private_subnets and _private_subnet_ids point to the same thing for those

cloud-deploy-infra/cloud/aws/templates/aws_oidc/vpc.tf

Line 19 in d5c99d3

vpc_public_subnets = local.enable_managed_vpc ? module.vpc[0].public_subnets : data.aws_subnets.external_public_subnets

Checklist

General

• Added the correct label
• Assigned to a specific person or civiform/deployment-system
• Performed manual testing (at a minimum run bin/setup without your changes and then bin/deploy with your changes to ensure your changes don't break existing deployments)

Issue(s) this completes

civiform/civiform#8412