.ci/check/shellcheck.sh: introduced file

.ci/check/shellcheck.sh

+#!/bin/bash
+
+if [ -z "${SHELLCHECK_BIN}" ]; then
+    SHELLCHECK_BIN="shellcheck"
+fi
+
+if ! command -v "${SHELLCHECK_BIN}" >/dev/null 2>&1; then
+    echo "ERROR: Binary '${SHELLCHECK_BIN}' does not exist, please set the environment variable SHELLCHECK_BIN to the correct shellcheck version."
+    exit 1
+fi
+
+check_command="${SHELLCHECK_BIN}"
+
+check_script="$(dirname "${BASH_SOURCE[0]}")/check.sh"
+
+files_regex=".*\.sh$"
+
+if ! "${check_script}" --check-command "${check_command}" --files-regex "${files_regex}" "$@"; then
+    echo "ERROR: Executing '${check_script}' failed."
+    exit 1
+fi