start work on spotless -> checkstyle conversion

buildSrc/src/main/kotlin/webhooklogger.java-conventions.gradle.kts

@@ -1,6 +1,6 @@
 plugins {
 	java
-	id("com.diffplug.spotless")
+	checkstyle
 }
 
 group = rootProject.group
@@ -12,17 +12,10 @@ java.toolchain {
 }
 
 tasks {
+	build {
+		dependsOn(checkstyleMain)
+	}
 	compileJava {
 		options.encoding = "UTF-8"
 	}
-}
-
-spotless {
-	java {
-		endWithNewline()
-		formatAnnotations()
-		indentWithTabs()
-		removeUnusedImports()
-		trimTrailingWhitespace()
-	}
 }

config/checkstyle/checkstyle.xml

@@ -0,0 +1,35 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE module PUBLIC
+        "-//Checkstyle//DTD Checkstyle Configuration 1.3//EN"
+        "https://checkstyle.org/dtds/configuration_1_3.dtd">
+
+<module name="Checker">
+    <property name="charset" value="UTF-8"/>
+
+    <module name="TreeWalker">
+        <!-- Annotations -->
+        <module name="MissingOverride"/>
+
+        <!-- Block Checks -->
+        <module name="AvoidNestedBlocks"/>
+        <module name="EmptyBlock"/>
+        <module name="EmptyCatchBlock"/>
+        <module name="LeftCurly"/>
+        <module name="NeedBraces"/>
+        <module name="RightCurly"/>
+
+        <!-- Class Design -->
+        <module name="FinalClass"/>
+
+        <module name="RegexpSinglelineJava">
+            <property name="format" value="^\t* "/>
+            <property name="message" value="Indent must use tab characters"/>
+            <property name="ignoreComments" value="true"/>
+        </module>
+
+        <!-- Imports -->
+        <module name="IllegalImport"/>
+        <module name="RedundantImport"/>
+        <module name="UnusedImports"/>
+    </module>
+</module>