* metadata addon works

* Add code for metadata server image and makefile rules

* remove log message

* update to work with v1.13.11

* update readme

* fix metadata addon stuff for newer codebase

* buncha changes

* just so many changes

* ch-ch-ch-ch-changes

* addon works

* update readme

* boilerplate

* revert unrelated change

* move server code to another repo

* switch addon name to gcp-auth

* metadata -> gcp-auth

* missed one

* automate finding of credentials

* remove unnecessary comment

* address comments

* Update README.md

* Update README.md

* use mustload everywhere

* swap selector condition

* upgrade kube-webhook-certgen to 1.3

* move paths to constants

* add notice to user on addon enable

* adding addon documentation

* move addons documentation inside handbook

* remove old addons docs location
Co-authored-by: NPriya Wadhwa <priyawadhwa@google.com>

Whenever a `kubectl apply` fails while enabling an addon, it is
retried with exponential backoff. The command (type `*exec.Cmd`)
that this retry function runs in created outside the function -
which means that it is reused on every retry. This is a problem
because `exec.Cmd` (https://godoc.org/github.com/pkg/exec#Cmd)
states that "... Cmd cannot be reused after calling its Run or
Start methods."

This retry is a common case due to, say, a CRD and its resource
being present in the same YAML file of the addon which causes
a race condition where the resource is created before its CRD is
created in the cluster - this race is fixed by subsequent retries.
I've noticed this in the dashboard and the ambassador addon.

Due to the above mentioned bug, minikube throws errors like
`exec: already started` in every retry and the retry is never
successful, manifests are never deployed and addon creation errors
out.

Related to #8138 #8119 #8372

This is an easy way to improve overhead, and users can always scale this back up if they need to.

Create a new addon, `podsecuritypolicies` that applies the
PodSecurityPolicy and related RBAC configuration from the
https://minikube.sigs.k8s.io/docs/tutorials/using_psp/ tutorial.
Apparently, recent work on the addons system has invalidated the
procedure shown in that tutorial, as the configuration is no longer
automatically applied. The last known working version is `1.6.2`.

This allows clusters started with
`--extra-configs=apiserver.enable-admission-plugins=PodSecurityPolicy`
to succeed, so long as they also include `--addons=podsecuritypolicies`.