Automatic merge from submit-queue (batch tested with PRs 59723, 60379, 60329). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.
fix typo, this let's -> this lets
**What this PR does / why we need it**:
fix typo
**Release note**:
```release-note
NONE
```
Automatic merge from submit-queue (batch tested with PRs 58144, 57149). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.
make quota reusable
Quota is logically a re-useable component so that replenishment and admission can be done in constituent servers. This makes it possible to embed. More cleanup is probably required, but this is the minimum.
Automatic merge from submit-queue (batch tested with PRs 49856, 56257, 57027, 57695, 57432). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.
remove duplicated validation from pod's resourcequota admission
ResourceQuota is a validating admission plugin. Before it runs, pods
has already been validated. It's not necessary to validate it again.
**Release note**:
```release-note
NONE
```
Automatic merge from submit-queue
Remove null -> [] slice hack
Closes#44593
When 1.6 added protobuf storage, the storage layer lost the ability to persist slice fields with empty but non-null values.
As a workaround, we tried to convert empty slice fields to `[]`, rather than `null`. Compressing `null` -> `[]` was just as much of an API breakage as `[]` -> `null`, but was hoped to cause fewer problems in clients that don't do null checks.
Because of conversion optimizations around converting lists of objects, the `null` -> `[]` hack was discovered to only apply to individual get requests, not to a list of objects. 1.6 and 1.7 was released with this behavior, and the world didn't explode. 1.7 documented the breaking API change that `null` and `[]` should be considered equivalent, unless otherwise noted on a particular field.
This PR:
* Reverts the earlier attempt (https://github.com/kubernetes/kubernetes/pull/43422) at ensuring non-null json slice output in conversion
* Makes results of `get` consistent with the results of `list` (which helps naive clients that do deepequal comparisons of objects obtained via list/watch and get), and allows empty slice fields to be returned as `null`
```release-note
Protobuf serialization does not distinguish between `[]` and `null`.
API fields previously capable of storing and returning either `[]` and `null` via JSON API requests (for example, the Endpoints `subsets` field) can now store only `null` when created using the protobuf content-type or stored in etcd using protobuf serialization (the default in 1.6+). JSON API clients should tolerate `null` values for such fields, and treat `null` and `[]` as equivalent in meaning unless specifically documented otherwise for a particular field.
```
Automatic merge from submit-queue (batch tested with PRs 45346, 45903, 45958, 46042, 45975)
ResourceQuota admission control injects registry
**What this PR does / why we need it**:
The `ResourceQuota` admission controller works with a registry that maps a GroupKind to an Evaluator. The registry used in the existing plug-in is not injectable, which makes usage of the ResourceQuota plug-in in other API server contexts difficult. This PR updates the code to support late injection of the registry via a plug-in initializer.
this is a two stage refactor when done there will be no init block in admission plugins.
Instead all plugins expose Register function which accept admission.Plugins instance.
The registration to global plugin registry happens inside Register func.
