Update microsoft office365 plugin name to follow OSI naming convention (#6005)

Following the OSI naming convention to use underscore. microsoft office365 plugin name from microsoft-office365
to microsoft_office365.

Author: wjyao0316

data-prepper-plugins/saas-source-plugins/microsoft-office365-source/src/main/java/org/opensearch/dataprepper/plugins/source/microsoft_office365/utils/Constants.java

@@ -14,7 +14,7 @@
  * The type Constants.
  */
 public class Constants {
-    public static final String PLUGIN_NAME = "microsoft-office365";
+    public static final String PLUGIN_NAME = "microsoft_office365";
     public static final String[] CONTENT_TYPES = {
             "Audit.AzureActiveDirectory",
             "Audit.Exchange",