[v0.16.0] Default Admission Controllers

[dominicgunn]

Changes

• This PR explicitly lists the admission controllers enabled by default as described [here]https://v1-16.docs.kubernetes.io/docs/reference/access-authn-authz/admission-controllers/).
• We also remove the Initializer admission controller, it hasn't existed since Kubernetes v1.10.x.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
To complete the pull request process, please assign dominicgunn
You can assign the PR to them by writing /assign @dominicgunn in a comment when ready.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[codecov-commenter]

Codecov Report

Merging #1857 into master will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1857      +/-   ##
==========================================
+ Coverage   24.40%   24.42%   +0.01%     
==========================================
  Files          98       98              
  Lines        5117     5114       -3     
==========================================
  Hits         1249     1249              
+ Misses       3728     3725       -3     
  Partials      140      140              

Impacted Files	Coverage Δ
pkg/api/cluster.go	0.00% <ø> (ø)
pkg/api/types.go	0.00% <ø> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update bdc0325...9d5048a. Read the comment docs.

[dominicgunn]

/lgtm

[k8s-ci-robot]

@dominicgunn: you cannot LGTM your own PR.

In response to this:

/lgtm

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.