Use jenkins.baseline to match archetype (#59)

* Use dependabot config from archetype

* Avoid bom version mismatches with jenkins.baseline

The Jenkins plugin archetype uses jenkins.baseline to prevent
inconsistencies between the minimum required Jenkins version and the
Jenkins plugin bill of materials version.  Use the same technique in
this plugin.

Author: MarkEWaite

.github/dependabot.yml

@@ -1,15 +1,12 @@
-# To get started with Dependabot version updates, you'll need to specify which
-# package ecosystems to update and where the package manifests are located.
-# Please see the documentation for all configuration options:
-# https://help.github.com/github/administering-a-repository/configuration-options-for-dependency-updates
+# https://docs.github.com/code-security/dependabot/dependabot-version-updates/configuring-dependabot-version-updates
 
 version: 2
 updates:
-  - package-ecosystem: "maven"
-    directory: "/"
-    schedule:
-      interval: "monthly"
-  - package-ecosystem: "github-actions"
-    directory: "/"
-    schedule:
-      interval: "monthly"
+- package-ecosystem: maven
+  directory: /
+  schedule:
+    interval: monthly
+- package-ecosystem: github-actions
+  directory: /
+  schedule:
+    interval: monthly

pom.xml

@@ -51,7 +51,8 @@
 
   <properties>
     <changelist>999999-SNAPSHOT</changelist>
-    <jenkins.version>2.414.3</jenkins.version>
+    <jenkins.baseline>2.414</jenkins.baseline>
+    <jenkins.version>${jenkins.baseline}.3</jenkins.version>
     <gitHubRepo>jenkinsci/${project.artifactId}-plugin</gitHubRepo>
   </properties>
 
@@ -60,7 +61,7 @@
       <dependency>
         <!-- Pick up common dependencies for the selected LTS line: https://github.com/jenkinsci/bom#usage -->
         <groupId>io.jenkins.tools.bom</groupId>
-        <artifactId>bom-2.414.x</artifactId>
+        <artifactId>bom-${jenkins.baseline}.x</artifactId>
         <version>2982.vdce2153031a_0</version>
         <type>pom</type>
         <scope>import</scope>