Automatic merge from submit-queue

Add PriorityClass API object under new "scheduling" API group

**What this PR does / why we need it**: This PR is a part of a series of PRs to add pod priority to Kubernetes. This PR adds a new API group called "scheduling" with a new API object called "PriorityClass". PriorityClass maps the string value of priority to its integer value.

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #

**Special notes for your reviewer**: Given the size of this PR, I will add the admission controller for the PriorityClass in a separate PR.

**Release note**:

```release-note
Add PriorityClass API object under new "scheduling" API group
```

ref/ #47604
ref/ #48646

Automatic merge from submit-queue

Add a heap to client-go. Heap orders items with heap invariant ordering.

**What this PR does / why we need it**:
Heap is useful in implementing priority queues. Some components may need such ordering to process their highest priority objects first. Scheduler is going to be the first user of the heap. It will store pending pods ordered by their priority, so that the highest priority pods are popped first to be scheduled.

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #

**Special notes for your reviewer**:

**Release note**:

```release-note
NONE
```

ref/ #47604
ref/ #48646

@kubernetes/api-reviewers @kubernetes/sig-scheduling-pr-reviews @davidopp 
/assign @caesarxuchao

Automatic merge from submit-queue

Add Priority admission controller

**What this PR does / why we need it**: Add Priority admission controller. This admission controller checks creation and update of PriorityClasses. It also resolves a PriorityClass name of a pod to its integer value.

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #

**Special notes for your reviewer**:

**Release note**:

```release-note
Add Priority admission controller for monitoring and resolving PriorityClasses.
```

ref/ #47604
ref/ #48646

Automatic merge from submit-queue

Add support to modify precomputed predicate metadata upon adding/removal of a pod

**What this PR does / why we need it**: This PR adds capability to change precomputed predicate metadata and let's us add/remove pods to the precomputed metadata efficiently without the need ot recomputing everything upon addition/removal of pods. This PR is needed as a part of adding preemption logic to the scheduler.

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #

**Special notes for your reviewer**:
To make the review process a bit easier, there are three commits. The cleanup commit is only moving code and renaming some functions, without logic changes.

**Release note**:

```release-note
NONE
```
ref/ #47604
ref/ #48646

/assign @wojtek-t 

@kubernetes/sig-scheduling-pr-reviews @davidopp

Automatic merge from submit-queue

Add pod preemption to the scheduler

**What this PR does / why we need it**:
This is the last of a series of PRs to add priority-based preemption to the scheduler. This PR connects the preemption logic to the scheduler workflow.

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #48646

**Special notes for your reviewer**:
This PR includes other PRs which are under review (#50805, #50405, #50190). All the new code is located in 43627af.

**Release note**:

```release-note
Add priority-based preemption to the scheduler.
```

ref/ #47604

/assign @davidopp 

@kubernetes/sig-scheduling-pr-reviews