Sets link to hold panel to open in new tab

** Why are these changes being introduced:

* The link named "See details in admin interface" on the thesis
  processing form, in the status panel, has an undefined target. Staff
  users have requested that this link be forced to open in a new tab.

** Relevant ticket(s):

* https://mitlibraries.atlassian.net/browse/ETD-374

** How does this address that need:

* This explicitly sets the target of this link to be `_blank`, which
  will force well-designed browsers to open the link in a new tab.

** Document any side effects to this change:

* It will no longer be possible to open these links in the same tab.

app/views/thesis/process_theses.html.erb

@@ -50,7 +50,7 @@
                                       label_html: { style: 'width: 50%' },
                                       input_html: { class: 'disabled', style: 'width: 40%', value: f.object.active_holds?? 'Yes' : 'No' },
                                       hint_html: { style: 'display: block' },
-                                      hint: link_to('See details in admin interface',admin_thesis_path(f.object)) %>
+                                      hint: link_to('See details in admin interface', admin_thesis_path(f.object), target: :_blank) %>
 
         </li>
         <li>