Adding the following accross the project:

```bash
/# exit immediately when a command fails
set -e
/# only exit with zero if all commands of the pipeline exit successfully
set -o pipefail
/# error on unset variables
+set -u

```

The current example-app setup in the kube-prometheus project is able to
discover scraping targets in the default namespace. It is not able to
discover the configured Alertmanager in the monitoring namespace.

This patch adds an alertmanager-discovery rbac role, to permit the
above described action. In addition it does the following cleanups:

- Remove kubeconfig configuration in deploy and teardown script. kubectl
chooses .kube/config whenever KUBECONFIG is not set by default

- Remove namespace specification option via NAMESPACE env var. In most
of the manifests the metadata/namespace was hardcoded anyways, in
addition in the promtheus frontend role binding the service account
namespace is hardcoded to default as well.

- Instead of `kubectl {apply,delete}` individual manifests, the deploy
and teardown shell scripts {apply,delete} on the entire folder.

added service account, role and role binding for the prometheus frontend
example, also updated prometheus to use the correct service account

fixes #1049

https://github.com/kubernetes/kubernetes/issues/29542 has been fixed,
use apply instead of create to create third party resources in custom service
monitoring example.

git-subtree-dir: contrib/kube-prometheus
git-subtree-mainline: 050ca21276696c8603375c699513ec487301ed62
git-subtree-split: 81c0d2f4

There is an issue with kubectl apply and third party resources, so for
the time being we use create for TPRs, but apply for all manifests that
it can handle.