The Fast stage 2-networking-* currently adds a monitoring dashboard
for VPN metrics. This change adds an additional chart to monitor the
usage of the VPN bandwidth.
This change also adds the following monitoring alerts:
* VPN tunnel established
*
[VPN bandwidth](https://cloud.google.com/network-connectivity/docs/vpn/how-to/viewing-logs-metrics#define-bandwidth-alerts)
To configure the alerts, there is a new `alert_config` variable with
defined default values.
The alerts are created in the stage `b` by default. In the stages a,
c, d, and e, the alerts are created if the user creates the On-prem
VPN.
To disable the creation of alerts, add the following to
`terraform.tfvars`:
```
alert_config = {
vpn_tunnel_established = null
vpn_tunnel_bandwidth = null
}
```