Fix Micrometer-based deployment issues.

When deploying to artifactory, a Micrometer-based plugin can't be found.

See #4017.

spring-data-mongodb-distribution/pom.xml

@@ -121,4 +121,26 @@
     </repository>
   </repositories>
 
+  <pluginRepositories>
+    <pluginRepository>
+      <id>spring-snapshots</id>
+      <name>Spring Snapshots</name>
+      <url>https://repo.spring.io/snapshot</url> <!-- For Snapshots -->
+      <snapshots>
+        <enabled>true</enabled>
+      </snapshots>
+      <releases>
+        <enabled>false</enabled>
+      </releases>
+    </pluginRepository>
+    <pluginRepository>
+      <id>spring-milestones</id>
+      <name>Spring Milestones</name>
+      <url>https://repo.spring.io/milestone</url>  <!-- For Milestones -->
+      <snapshots>
+        <enabled>false</enabled>
+      </snapshots>
+    </pluginRepository>
+  </pluginRepositories>
+
 </project>