Automatic merge from submit-queue (batch tested with PRs 47700, 48464, 48502)
Provide a way to setup the limit NO files for rkt Pods
**What this PR does / why we need it**:
This PR allows to customize the Systemd unit files for rkt pods.
We start with the `systemd-unit-option.rkt.kubernetes.io/LimitNOFILE` to allows to run workloads like etcd, ES in kubernetes with rkt.
**Special notes for your reviewer**:
Once again, I followed @yifan-gu guidelines.
I made a basic check over the values given inside the `systemd-unit-option.rkt.kubernetes.io/LimitNOFILE` (integer and > 0).
If this check fails: I simply ignore the field.
The other implementation would be to fail the whole SetUpPod.
We discussed using a key like `rkt.kubernetes.io/systemd-unit-option/LimitNOFILE` but the validation only allows a single `/` in this field:
```The Deployment "tiller" is invalid: spec.template.annotations: Invalid value: "rkt.kubernetes.io/systemd-unit-option/LimitNOFILE": a qualified name must consist of alphanumeric characters, '-', '_' or '.', and must start and end with an alphanumeric character (e.g. 'MyName', or 'my.name', or '123-abc', regex used for validation is '([A-Za-z0-9][-A-Za-z0-9_.]*)?[A-Za-z0-9]') with an optional DNS subdomain prefix and '/' (e.g. 'example.com/MyName')```
**Release note**:
```release-note
NONE
```
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