This adds an interface form of dynamic.Client and
dynamic.ResourceClient, making those two follow the general client
conventions: `Interface` is an interface, and `Client` is the concrete
implementation. `ClientPool` retains it's interface status.
This allows us to create a fake implemenation of dyanmic.Interface,
dynamic.ResourceInterface, and dynamic.ClientPool for testing.
Allow the list of resources the garbage collector controller should
ignore to be customizable, so downstream integrators can add their own
resources to the list, if necessary.
Automatic merge from submit-queue (batch tested with PRs 40055, 42085, 44509, 44568, 43956)
Fix gofmt errors
**What this PR does / why we need it**:
There were some gofmt errors on master. Ran the following to fix:
```
hack/verify-gofmt.sh | grep ^diff | awk '{ print $2 }' | xargs gofmt -w -s
```
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: none
**Special notes for your reviewer**:
**Release note**:
```release-note
NONE
```
