Issue #3421721 Added PHPCS configuration file

.phpcs.xml

+<?xml version="1.0"?>
+<ruleset xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" name="drupal/commerce_sheets" xsi:noNamespaceSchemaLocation="phpcs.xsd">
+    <description>The coding standard for the Commerce Sheets module.</description>
+
+    <file>src</file>
+
+    <!-- Include the Drupal and DrupalPractice standards -->
+    <rule ref="Drupal">
+        <!-- We sort use statements alphabetically, but group them in sections when there are too many -->
+        <exclude name="SlevomatCodingStandard.Namespaces.AlphabeticallySortedUses"/>
+    </rule>
+    <rule ref="DrupalPractice"></rule>
+
+    <!-- Correct indentation in class declarations -->
+    <rule ref="Drupal.Classes.ClassDeclaration">
+        <properties>
+            <property name="indent" value="2" /> -->
+        </properties>
+    </rule>
+
+</ruleset>