feat: add runner-template stack

[jhatler]

This stack is used to define launch templates in AWS for creating GitHub Actions runners.

Refs: #362

[infracost[bot]]

💰 Infracost report

Monthly estimate generated

Estimate details (includes details of unsupported resources)

``` ────────────────────────────────── 10 projects have no cost estimate changes. Run the following command to see their breakdown: infracost breakdown --path=/path/to/code ────────────────────────────────── 166 cloud resources were detected: ∙ 15 were estimated ∙ 138 were free ∙ 13 are not supported yet, see https://infracost.io/requested-resources: ∙ 10 x aws_network_acl_association ∙ 3 x aws_s3_bucket_lifecycle_configuration ```

_{This comment will be updated when code changes.}