C210K: scaletest github action

### Overview
Need a github action to run the scaletest and show pass/fail.

### Tasks
- [ ] Github action accepts any number of users to set infra sizing
- At what increment?'
- [ ] Action executes terraform apply
- [ ] Test data is pushed to prometheus
- [ ] outputs links to Grafana dashboards
- [ ] Outputs pass/fail for the test
- [ ] outputs errors when hit
- [ ] Spins down infrastructure

Start with the requested GitHub Action and the task list in this issue. Clarify the user-count increment and the scaletest entry point before implementation. Done means the action sizes infrastructure, applies Terraform, publishes test data to Prometheus, links Grafana dashboards, reports pass/fail and errors, and spins infrastructure down.

Written by the indexing model from the issue text.