[DMN Designer] Multiple DRDs Support - Show an interaction icon when users select more than one DMN element

When users select more than one DMN element:

We must display an interaction icon, like this one:

⚠️ Notice:

• The correct icon is the *sitemap* https://fontawesome.com/icons/sitemap?style=solid, https://issues.jboss.org/browse/DROOLS-3566?focusedCommentId=13804999&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-13804999
• We shouldn't show the icon when the selection has only one element (since we will have the *sitemap* icon for individual nodes)
• This JIRA doesn't comprehends any action. The interaction with this icon will be covered by DROOLS-4781