ci: Add basic shellcheck, whitespace & format checks

ci/shellcheck

@@ -0,0 +1,35 @@
+#!/bin/bash
+# Template generated by https://github.com/coreos/repo-templates; do not edit downstream
+
+set -euo pipefail
+
+main() {
+    local found_errors="false"
+    # Let's start with error, then we can do warning, info, style
+    local -r severity="error"
+
+    while IFS= read -r -d '' f; do
+        # Skip non-text files that are very unlikely to be shell scripts
+        if [[ "$(file -b --mime-type "${f}" | sed 's|/.*||')" != "text" ]]; then
+            continue
+        fi
+        shebang="$(head -1 "${f}")"
+        if [[ "${f}" == *.sh ]] || \
+            [[ ${shebang} =~ ^#!/.*/bash.* ]] || \
+            [[ ${shebang} =~ ^#!/.*/env\ bash ]]; then
+            echo "[+] Checking ${f}"
+            shellcheck --external-sources --shell bash --severity="${severity}" "${f}" || found_errors="true"
+            bash -n "${f}" || found_errors="true"
+        fi
+    done< <(find . -path "./.git" -prune -o -path "./vendor" -prune -o -type f -print0)
+
+    if [[ "${found_errors}" != "false" ]]; then
+        echo "[+] Found errors with ShellCheck"
+        exit 1
+    fi
+
+    echo "[+] No error found with ShellCheck"
+    exit 0
+}
+
+main "${@}"