Signed-off-by: Daniel Dao <[email protected]>

This adds 2 new set of metrics:
- `psi_total`: read total number of seconds a resource is under pressure
- `psi_avg`: read ratio of time a resource is under pressure over a
  sliding time window.

For more details about these definitions, see:
- https://www.kernel.org/doc/html/latest/accounting/psi.html
- https://facebookmicrosites.github.io/psi/docs/overview

Signed-off-by: Daniel Dao <[email protected]>

This adds support for reading PSI metrics via prometheus. We exposes the
following for `psi_total`:

```
container_cpu_psi_total_seconds
container_memory_psi_total_seconds
container_io_psi_total_seconds
```

And for `psi_avg`:

```
container_cpu_psi_avg10_ratio
container_cpu_psi_avg60_ratio
container_cpu_psi_avg300_ratio

container_memory_psi_avg10_ratio
container_memory_psi_avg60_ratio
container_memory_psi_avg300_ratio

container_io_psi_avg10_ratio
container_io_psi_avg60_ratio
container_io_psi_avg300_ratio
```

Signed-off-by: Daniel Dao <[email protected]>