[enh] CI - add shell script formatter

Implement rules and functions to format shell scripts:

    $ make format.shell

or alternatively to format all source code:

    $ make format

The formatter `shfmt` reads the rules from the editorconfig[1]

  If any EditorConfig files are found, they will be used to apply formatting
  options.  If any parser or printer flags are given to the tool, no
  EditorConfig files will be used.

[1] https://github.com/patrickvane/shfmt?tab=readme-ov-file#description

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

manage

@@ -64,6 +64,12 @@ RST_FILES=(
     'README.rst'
 )
 
+SHFMT_SCRIPTS=(
+    "./manage"
+    "./container"
+    "./utils"
+)
+
 help() {
     nvm.help
     cat <<EOF
@@ -90,6 +96,7 @@ pyenv.:
   OK        : test if virtualenv is OK
 format.:
   python    : format Python code source using black
+  shell     : format Shell scripts using shfmt
 EOF
     go.help
     node.help
@@ -248,11 +255,17 @@ pyenv.uninstall() {
 }
 
 format.python() {
-    build_msg TEST "[format.python] black \$BLACK_TARGETS"
+    build_msg TEST "[format.python] black ${BLACK_TARGETS[*]}"
     pyenv.cmd black "${BLACK_OPTIONS[@]}" "${BLACK_TARGETS[@]}"
     dump_return $?
 }
 
+format.shell() {
+    build_msg TEST "[shfmt] shfmt ${SHFMT_SCRIPTS[*]}"
+    go.tool shfmt --list --write "${SHFMT_SCRIPTS[@]}"
+    dump_return $?
+}
+
 docs.prebuild() {
     build_msg DOCS "build ${DOCS_BUILD}/includes"
     (