Refactor the kube-scheduler configuration API, command setup, and server
setup according to the guidelines established in #32215 and using the
kube-proxy refactor (#34727) as a model of a well factored component
adhering to said guidelines.
* Config API: clarify meaning and use of algorithm source by replacing
modality derived from bools and string emptiness checks with an explicit
AlgorithmSource type hierarchy.
* Config API: consolidate client connection config with common structs.
* Config API: split and simplify healthz/metrics server configuration.
* Config API: clarify leader election configuration.
* Config API: improve defaulting.
* CLI: deprecate all flags except `--config`.
* CLI: port all flags to new config API.
* CLI: refactor to match kube-proxy Cobra command style.
* Server: refactor away configurator.go to clarify application wiring.
* Server: refactor to more clearly separate wiring/setup from running.
Fixes#52428.
Automatic merge from submit-queue (batch tested with PRs 52723, 53271). 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>.
Apply algorithm in scheduler by feature gates.
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: part of #42001
**Release note**:
```release-note
Apply algorithm in scheduler by feature gates.
```
Automatic merge from submit-queue (batch tested with PRs 51574, 51534, 49257, 44680, 48836)
update scheduler to return structured errors instead of process exit
The scheduler Run method returns an error that is properly handled at higher levels. Instead of existing the process, we should return the error and handle it at higher level logic to allow testing of error conditions and composition of commands. The changes are relatively minor.
@sjenning @aveshagarwal
Previously, the scheduler created two separate list watchers. This
changes the scheduler to be able to leverage a shared informer, whether
passed in externally or spawned using the new in place method. This
removes the last use of a "special" informer in the codebase.
Allows someone wrapping the scheduler to use a shared informer if they
have more information avaliable.
Where possible, switch the scheduler to use generated listers and
informers. There are still some places where it probably makes more
sense to use one-off reflectors/informers (listing/watching just a
single node, listing/watching scheduled & unscheduled pods using a field
selector).
Automatic merge from submit-queue (batch tested with PRs 39538, 40188, 40357, 38214, 40195)
Decoupling scheduler creation from creation of scheduler.Config struc…
**What this PR does / why we need it**:
Adds functionality to the scheduler to initialize from an Configurator interface, rather then via a Config struct.
**Which issue this PR fixes**
Reduces coupling to `scheduler.Config` data structure format so that we can proliferate more interface driven composition of scheduler components.
Automatic merge from submit-queue (batch tested with PRs 36263, 36755, 37357, 37222, 37524)
Add flag to enable contention profiling in scheduler.
```release-note
Add flag to enable contention profiling in scheduler.
```
