This makes `make gardenadm-high-touch-up` idempotent. Without this,
multiple invocations result in:

```
root@machine-0:/# ls -al /gardenadm/resources/
total 12
drwxr-xr-x 2 root root  4096 Mar 17 14:04 .
drwxrwxrwx 3 root root  4096 Mar 17 14:04 ..
-rw-r--r-- 1  501 staff 2584 Mar 17 14:04 manifests.yaml
```

now run `make gardenadm-high-touch-up` again
result:

```
root@machine-0:/# ls -al /gardenadm/resources/
total 16
drwxr-xr-x 3 root root  4096 Mar 17 14:12 .
drwxrwxrwx 3 root root  4096 Mar 17 14:04 ..
-rw-r--r-- 1  501 staff 2584 Mar 17 14:04 manifests.yaml
drwxr-xr-x 2 root root  4096 Mar 17 14:12 resources
```

We were already doing this for `garden.local.gardener.cloud:5001`, but
now we also need the other mirrors. Hence, let's just add all of them to
the `Dockerfile` directly (this way, we can drop the webhook in
`provider-local` which mutates the `OperatingSystemConfig` and
configures the mirrors there).

- we will deploy two etcds (main and events) even for bootstrapping to
  remain as close to the target picture as possible
- on the way, we fixed a few minor issues that prevented etcd from
  starting up

This partially reverts gardener@41c09fe.

This will only be used for bootstrapping the autonomous shoot cluster
control plane (i.e., only short-term, and only for bringing up the
components initially).

- plus helper func for fetching the control plane worker pool
- specify network settings (now that we have a control-plane worker pool, `botanist.DefaultNetwork` is called).
  Without this, this will fail with:

  ```
  panic: runtime error: invalid memory address or nil pointer dereference
  [signal SIGSEGV: segmentation violation code=0x1 addr=0x8 pc=0x19abfb4]

  goroutine 1 [running]:
  github.com/gardener/gardener/pkg/gardenlet/operation/botanist.(*Botanist).DefaultNetwork(0x400080aef8)
  	github.com/gardener/gardener/pkg/gardenlet/operation/botanist/network.go:27 +0x304
  ...
  ```

- set `failSwapOn=false` for local shoot (for regular shoots, provider-local usually injects the `failSwapOn`, but it is not running here)
- also use other kubelet configs from https://github.com/gardener/gardener/blob/be88429ebd3288c3a17f5e9351d883e8a6ed2650/example/provider-local/shoot.yaml#L29-L36

- in addition, make sure shoot networks are set

  This is usually called separately in the reconciliation flows: https://github.com/gardener/gardener/blob/e5b022d637bbf52dcb427e52fbce45e1eb18e220/pkg/gardenlet/controller/shoot/shoot/reconciler_reconcile.go#L127-L131

- embeds shoot's `Botanist` struct
- will carry methods for bootstrapping an autonomous shoot

Earlier, this was only populated in `Wait`, but we can move the static
data up to `Deploy`/`Restore`. In the `gardenadm init` flow, there is no OSC
controller, i.e., we will not call `Wait` anyways.

In high-touch, the machines are already set-up/Gardener does not control
the operating system. Hence, we specifying it in the `ShootSpec` should
not be mandatory.

- without this, the containers cannot read the files from the host
  (mounted via `hostPath`)

Without this:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x8 pc=0x197e774]

goroutine 13 [running]:
github.com/gardener/gardener/pkg/gardenlet/operation/shoot.(*Shoot).ComputeOutOfClusterAPIServerAddress(0x0?, 0x0?)
	github.com/gardener/gardener/pkg/gardenlet/operation/shoot/shoot.go:511 +0x194
github.com/gardener/gardener/pkg/gardenlet/operation/botanist.(*Botanist).DeployKubeAPIServer(0x40005dac90, {0x2932cf8, 0x400090d090}, 0x0)
	github.com/gardener/gardener/pkg/gardenlet/operation/botanist/kubeapiserver.go:165 +0x40
...

For static pods, we inject this as host alias to resolve to localhost
(they cannot directly resolve `kubernetes.default.svc` because they don't
talk to the cluster DNS (CoreDNS))

For regular shoots, provider-local's webhook on OperatingSystemConfig
injects the `/ko-app` prefix. However, in the gardenadm scenario, we
don't have provider-local's webhook, so the only feasible option is to
handle it ourselves. Not nice, but perhaps the most pragmatic solution.

We might have to do the same for the gardener-node-init script later
when we implement `gardenadm` join (then we can drop the webhook in
provider-local for good).

similar to kubeadm (ref https://kubernetes.io/docs/setup/production-environment/tools/kubeadm/create-cluster-kubeadm/)

- also adapt e2e test with a simple assertion