*.sh: Set sane bash options on shell scripts

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

```

experimental/custom-metrics-api/gencerts.sh

@@ -1,4 +1,10 @@
 #!/usr/bin/env 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
 
 # Detect if we are on mac or should use GNU base64 options
 case $(uname) in

hack/example-service-monitoring/deploy

@@ -1,3 +1,9 @@
 #!/usr/bin/env 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
 
 kubectl apply -f examples/example-app

hack/example-service-monitoring/teardown

@@ -1,3 +1,9 @@
 #!/usr/bin/env 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
 
 kubectl delete -f examples/example-app