contrib: add "nm-code-format-container.sh" to reformat working directory in container

We use clang-format to format our code, and the exact format depends on
the clang version. Currently we use clang-11, as packaged in Fedora 33.

Add a script that runs a Fedora 33 container with podman and reformats
the current working directory.

Usage:

  ./contrib/scripts/nm-code-format-container.sh

contrib/scripts/nm-code-format-container.sh

@@ -0,0 +1,45 @@
+#!/bin/bash
+
+set -e
+
+die() {
+    echo "$@" >&2
+    exit 1
+}
+
+DIR="$(realpath "$(dirname "$0")/../../")"
+cd "$DIR"
+
+PODNAME=nm-code-format
+
+RENEW=0
+for a; do
+    case "$a" in
+        -f)
+            RENEW=1
+            ;;
+        *)
+            die "invalid argument \"$a\""
+            ;;
+    esac
+done
+
+set -x
+
+if [ "$RENEW" == 1 ]; then
+    if podman container exists "$PODNAME" ; then
+        podman rm "$PODNAME"
+    fi
+fi
+
+if ! podman container exists "$PODNAME" ; then
+    podman run \
+        --name="$PODNAME" \
+        -v "$DIR:/tmp/NetworkManager:Z" \
+        -w /tmp/NetworkManager \
+        fedora:33 \
+        /bin/bash -c 'dnf upgrade -y && dnf install -y git which /usr/bin/clang-format && ./contrib/scripts/nm-code-format.sh -i'
+    exit 0
+fi
+
+podman start -a "$PODNAME"