Error out nicely if podman is not present

If podman is not installed we get the following unfriendly output:
[michele@rhel1]~/multicloud-gitops% ./pattern.sh
./pattern.sh: line 10: podman: command not found
./pattern.sh: line 10: podman: command not found
./pattern.sh: line 32: podman: command not found

Let's bail out and have a generic function to check for that in case
we need to add other requirements

Author: mbaldessari

scripts/pattern-util.sh

@@ -1,9 +1,15 @@
 #!/bin/bash
+function is_available {
+  command -v $1 >/dev/null 2>&1 || { echo >&2 "$1 is required but it's not installed. Aborting."; exit 1; }
+}
 
 if [ -z "$PATTERN_UTILITY_CONTAINER" ]; then
 	PATTERN_UTILITY_CONTAINER="quay.io/hybridcloudpatterns/utility-container"
 fi
 
+readonly commands=(podman)
+for cmd in ${commands[@]}; do is_available "$cmd"; done
+
 UNSUPPORTED_PODMAN_VERSIONS="1.6 1.5"
 for i in ${UNSUPPORTED_PODMAN_VERSIONS}; do
 	# We add a space