Add markdown formatter plugin (#3090)

Proposed wider use to document Pipeline shared libraries

jenkinsci/pipeline-groovy-lib-plugin#117

Has 860 installations with that number increasing steadily.

https://plugins.jenkins.io/pegdown-formatter/ should be deprecated. It
was last released 12 years ago.  It has a known security vulnerability.
It has no maintainer.  It has a health score of 57/100.  Still has over
1000 installations, but many of those installations could use markdown
formatter.

Author: MarkEWaite

bom-2.414.x/pom.xml

@@ -87,6 +87,11 @@
         <artifactId>json-path-api</artifactId>
         <version>2.9.0-33.v2527142f2e1d</version>
       </dependency>
+      <dependency>
+        <groupId>io.jenkins.plugins</groupId>
+        <artifactId>markdown-formatter</artifactId>
+        <version>95.v17a_965e696ee</version>
+      </dependency>
       <dependency>
         <groupId>io.jenkins.plugins</groupId>
         <artifactId>plugin-util-api</artifactId>

bom-weekly/pom.xml

@@ -353,6 +353,11 @@
         <artifactId>mariadb-api</artifactId>
         <version>3.3.3-31.v2fb_e19b_1802e</version>
       </dependency>
+      <dependency>
+        <groupId>io.jenkins.plugins</groupId>
+        <artifactId>markdown-formatter</artifactId>
+        <version>167.v8a_428ca_49f89</version>
+      </dependency>
       <dependency>
         <groupId>io.jenkins.plugins</groupId>
         <artifactId>mysql-api</artifactId>

sample-plugin/pom.xml

@@ -316,6 +316,11 @@
       <artifactId>mariadb-api</artifactId>
       <scope>test</scope>
     </dependency>
+    <dependency>
+      <groupId>io.jenkins.plugins</groupId>
+      <artifactId>markdown-formatter</artifactId>
+      <scope>test</scope>
+    </dependency>
     <dependency>
       <groupId>io.jenkins.plugins</groupId>
       <artifactId>mysql-api</artifactId>