Use jenkins.baseline for plugin BOM version (#113)

Reduce duplication in the pom file and make the plugin pom file closer
to the archetype.

Author: MarkEWaite

pom.xml

@@ -33,7 +33,8 @@
   <properties>
     <revision>3.4.1</revision>
     <changelist>999999-SNAPSHOT</changelist>
-    <jenkins.version>2.452.4</jenkins.version>
+    <jenkins.baseline>2.452</jenkins.baseline>
+    <jenkins.version>${jenkins.baseline}.4</jenkins.version>
     <gitHubRepo>jenkinsci/${project.artifactId}-plugin</gitHubRepo>
     <hpi.compatibleSinceVersion>3.2</hpi.compatibleSinceVersion>
     <spotless.check.skip>false</spotless.check.skip>
@@ -43,7 +44,7 @@
     <dependencies>
       <dependency>
         <groupId>io.jenkins.tools.bom</groupId>
-        <artifactId>bom-2.452.x</artifactId>
+        <artifactId>bom-${jenkins.baseline}.x</artifactId>
         <version>3790.va_b_a_2d26d2b_69</version>
         <type>pom</type>
         <scope>import</scope>