feature: support for checking against HTTP status code

# Description

The integrated [healthcheck](https://registry.terraform.io/providers/coder/coder/latest/docs/resources/app#nested-schema-for-healthcheck) should be able to check a HTTP a status code.

E.g. we are deploying an K3D cluster inside out workspace. The healthcheck is already green but user facing a 404 error page from kubernetes as the app is not up and running. Checking against a status code 200 should solve this.

Setting a explicit statuscode should change the default checking.

```hcl
resource "coder_app" "code-server" {
agent_id = coder_agent.dev.id
slug = "code-server"
display_name = "VS Code"
icon = "${data.coder_workspace.me.access_url}/icon/code.svg"
url = "http://localhost:13337"
share = "owner"
subdomain = false
healthcheck {
url = "http://localhost:13337/healthz"
interval = 5
threshold = 6
statuscode = 200
}
}
```

### Expected Behavior
Button should be enabled when application is ready and not when kubernetes cluster has started. If a statuscode 200 is set then the button gets enabled when the application is ready.

### Actual Behavior
As soon kubernetes cluster is ready the healtcheck is green and buttons are enabled