Add script which can be used to build affected modules only (#11461)

Motivation:

At the moment we always build all modules. This script can be used to only build affected modules for a given change

Modifications:

Add script that will only build modules that are affected by a change

Result:

More targeted build

.github/scripts/build_affected_only.sh

@@ -0,0 +1,33 @@
+#!/bin/bash
+# ----------------------------------------------------------------------------
+# Copyright 2021 The Netty Project
+#
+# The Netty Project licenses this file to you under the Apache License,
+# version 2.0 (the "License"); you may not use this file except in compliance
+# with the License. You may obtain a copy of the License at:
+#
+#   https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+# ----------------------------------------------------------------------------
+set -e
+
+if [ "$#" -lt 2 ]; then
+    echo "Expected branch and maven arguments"
+    exit 1
+fi
+
+MODULES=$(git diff --name-only "$1" | cut -d '/' -f 1 | sort -u | sed -n -e 'H;${x;s/\n/,/g;s/^,//;p;}')
+MAVEN_ARGUMENTS=${*:2}
+if [ -z "$MODULES" ]; then
+  echo "No changes detected, skipping build"
+  exit 0
+fi
+echo "Changes detected, start the build"
+echo "./mvnw -pl $MODULES -amd $MAVEN_ARGUMENTS"
+./mvnw -pl "$MODULES" -amd "${@:2}"
+