Fix checkstyle config to use relative path for suppressions

- Changed from ${basedir}/etc/checkstyle/suppressions.xml to etc/checkstyle/suppressions.xml
- Fixes checkstyle configuration parsing error where ${basedir} property was not resolved
- Local validate phase now passes successfully

Author: shahar-biron

etc/checkstyle/config.xml

@@ -21,7 +21,7 @@
 		"https://checkstyle.org/dtds/configuration_1_3.dtd">
 <module name="com.puppycrawl.tools.checkstyle.Checker">
 	<module name="SuppressionFilter">
-		<property name="file" value="${basedir}/etc/checkstyle/suppressions.xml"/>
+		<property name="file" value="etc/checkstyle/suppressions.xml"/>
 	</module>
 	<module name="io.spring.javaformat.checkstyle.SpringChecks">
 		<property name="excludes" value="io.spring.javaformat.checkstyle.check.SpringAvoidStaticImportCheck"/>